How long can the police check text messages and phone calls?

Generally within 6 months. The public security bureau can find short messages, but it can't just check them. People's Republic of China (PRC) citizens' freedom and privacy of communication are protected by law.

When public security organs and procuratorial organs check communication according to the procedures prescribed by law, no organization or individual may infringe upon citizens' freedom and privacy of communication for any reason, except for the needs of national security or criminal investigation.

Criminal procedure law

Article 148 After putting a case on file, the public security organ may, according to the needs of investigating crimes and through strict approval procedures, take technical investigation measures against crimes endangering national security, terrorist activities, organized crimes of underworld nature, major drug crimes or other crimes seriously endangering society.

Technical reconnaissance measures include electronic monitoring, telephone monitoring, electronic monitoring, secret photography, video recording, mail inspection and other secret special technical means, and naturally short message inquiry can also be carried out.