legal ground
Article 238 of the Criminal Procedure Law of People's Republic of China (PRC).
If the people's court of second instance finds that the trial of the people's court of first instance violates one of the following legal procedures, it shall make a ruling to revoke the original judgment and send it back to the people's court that originally tried it for retrial:
(a) in violation of the provisions of this law on public trial;
(2) Violating the challenge system;
(3) depriving or restricting the legal litigation rights of the parties, which may affect the fair trial;
(4) The composition of the judicial organization is illegal;
(five) other violations of the law, which may affect the fair trial.