Sun, who also served a three-month doping suspension in 2014, was found guilty of refusing to give a doping sample and banned for eight years by the Court of Arbitration for Sport (CAS) in February, upholding an appeal by the World Anti-Doping Agency (WADA) against swimming’s governing body FINA.
All decisions made by CAS can be appealed to the SFT.
Unless he is successful with the appeal, Sun will not be eligible for the Tokyo Games in 2021 and his career would be effectively over.
The SFT did not confirm the information, but according to the report, “a case file has been opened with a number attached to the ‘Sun Yang Case'”.
Magazine Swimming World reported on Monday that Sun’s lawyers had filed the appeal with a day to spare on April 29.
The three-time Olympic champion has previously seen two appeals rejected by the SFT before the CAS decision.
A vial of Sun’s own blood sample was smashed with a hammer during a testing session in 2018, but the swimmer was acquitted by FINA of anti-doping violations, agreeing that testers had failed to produce adequate identification.
But the ruling outraged WADA which took the matter to CAS, demanding a ban of between two and eight years for missing the out-of-competition test.
The Chinese Swimming Association (CSA) said after CAS announced Sun’s ban that it supported the 28-year-old and encouraged Sun to “continue to safeguard his legitimate rights”.
Sun has been widely criticised by other swimmers, with some rivals refusing to share a podium with him during the 2019 world championships.
Last month, WADA demanded answers after Sun was called up for national training for the Tokyo Olympics in an apparent breach of his ban.
The CSA said the notice naming Sun for the training was “invalid”.
Sun has kept a low profile since he was banned.