| ITF China F8 | 06/08 02:50 | 27 | [298] Fajing Sun v Zhe Li [322] | 6-2,3-6,2-6 | |
| ITF China F8 | 06/07 02:00 | 26 | Fajing Sun v William Ma | 6-1,6-1 | |
| ITF China F8 | 06/04 02:00 | 25 | Fajing Sun v Liran Chen | 6-4,6-3 | |
| ITF China F7 | 05/30 02:30 | 26 | [298] Fajing Sun v Zhe Li [322] | 5-7,4-6 | |
| ITF China F7 | 05/29 03:30 | 25 | Hao Wu v Fajing Sun | 6-2,2-6,2-6 | |
| ITF China F6 | 05/20 02:30 | 29 | [475] Patrik Niklas-Salminen v Fajing Sun [309] | 2-6,6-4,6-4 | |
| ITF China F6 | 05/19 03:00 | 28 | Kento Takeuchi v Fajing Sun | 1-6,3-6 | |
| ITF China F6 | 05/18 02:00 | 27 | Fajing Sun v Rigele Te | Retired | |
| ITF China F6 | 05/17 02:00 | 26 | [221] Xin Gao v Fajing Sun [309] | 3-6,3-6 | |
| ITF China F6 | 05/15 02:00 | 25 | Fajing Sun v Tsung-Hao Huang | 6-1,6-2 | |
| ITF China F5 | 05/09 02:00 | 25 | Fajing Sun v Sami Reinwein | 2-6,3-6 | |
| ITF China F4 | 05/04 03:00 | 27 | Fajing Sun v Rigele Te | 6-7,2-6 | |
| ITF China F4 | 05/02 03:00 | 26 | Fajing Sun v Zihao Xia | 2-6,6-3,6-3 | |
| ITF China F4 | 04/30 05:20 | 25 | Fajing Sun v Haitong Xia | 6-2,6-3 | |
| ITF Uzbekistán F1 | 04/16 09:00 | 25 | [330] Fajing Sun v Roman Safiullin [381] | 2-6,4-6 | |
| ITF Catar F3 | 03/15 11:30 | 27 | Fajing Sun v Daniel Altmaier | 1-6,3-6 | |
| ITF Catar F3 | 03/14 12:00 | 26 | Fajing Sun v Dominik Kellovsky | 6-1,6-4 | |
| ITF Catar F3 | 03/13 12:00 | 25 | Fajing Sun v Mousa Shanan Zayed | 6-1,6-0 | |
| ITF Catar F2 | 03/08 14:45 | 27 | Fajing Sun v Marsel Ilhan | 4-6,0-6 | |
| ITF Catar F2 | 03/07 13:05 | 26 | Fajing Sun v Adam El Mihdawy | 6-1,6-1 | |
| ITF Catar F2 | 03/06 15:40 | 25 | Fajing Sun v Jabor Al Mutawa | 6-0,6-1 | |
| ITF Catar F1 | 03/03 13:00 | 29 | Scott Griekspoor v Fajing Sun | 6-4,6-3 | |
| ITF Catar F1 | 03/02 12:00 | 28 | Fajing Sun v Omar Giacalone | 6-1,2-6,6-4 | |
| ITF Catar F1 | 03/01 12:00 | 27 | Fajing Sun v Pietro Rondoni | 6-1,6-0 | |
| ITF Catar F1 | 02/28 12:00 | 26 | Fajing Sun v Zizou Bergs | 6-1,7-6 | |
| ITF Catar F1 | 02/27 12:00 | 25 | Fajing Sun v Fred Simonsson | 7-5,6-2 | |
| ITF Hong Kong F5 | 12/25 02:00 | 25 | Nicholas S. Hu v Fajing Sun | 6-4,6-4 | |
| ITF Hong Kong F4 | 12/19 03:35 | 25 | [495] Fajing Sun v Yan Bai [444] | 3-6,2-6 | |
| ITF Tailandia F12 | 12/13 03:00 | 26 | [172] Alexey Vatutin v Fajing Sun [488] | 6-1,6-3 | |
| ITF Tailandia F12 | 12/12 03:00 | 25 | Matteo Martineau v Fajing Sun | Retired |
Sun Fajing (Chinese: 孙发京; pinyin: Sūn Fājīng; Mandarin pronunciation: [swə́n fá tɕíŋ]; born 3 October 1996) is a Chinese tennis player.
Sun has a career high ATP singles ranking of world No. 351 achieved on 10 February 2020. He also has a career high ATP doubles ranking of world No. 181 achieved on 26 February 2024. He has reached 13 career singles finals posting a record of 5 wins and 8 losses, all coming on the ITF Futures tour. Additionally, he has reached 31 doubles finals posting a record of 16 wins and 15 losses, which includes 2 ATP Challenger Tour doubles titles.
Sun made his ATP main draw debut at the 2016 Chengdu Open, where he was granted a wildcard entry in the doubles draw alongside compatriot He Yecong. They were defeated in the first round by Raven Klaasen and Rajeev Ram in straight sets 4–6, 5–7.
The following year, he was again given a wildcard at the 2017 Chengdu Open with partner Te Rigele, and again he would lose in the first round to Nenad Zimonjic and Santiago Gonzalez in straight sets 4–6, 4–6.
In his third main draw appearance, he and partner Zhizhen Zhang were given a wildcard entry into the doubles draw of the 2018 ATP Shenzhen Open but lost in the first round to Marcin Matkowski and Nicholas Monroe 4–6, 2–6.
His fourth and most recent ATP appearance (also his third at the tournament) was a wildcard entry into the doubles draw of the 2019 Chengdu Open pairing up with Wang Aoran, and to round up an 0–4 record he lost to Dominic Inglot and Austin Krajicek 1–6, 6–0, [8–10].
He was given a wildcard at the 2023 China Open (tennis) partnering Zhou Yi (tennis). He received also a wildcard in doubles partnering Li Zhe (tennis) at the 2023 Rolex Shanghai Masters.