The public security bureau can check the contents of short messages for a few years at most.

Legal analysis: How many years ago the short message information can be found by the public security system is a technical problem. It should be analyzed concretely and concretely. However, our freedom of communication and communication secrets are protected by law and cannot be viewed at will.

Legal basis: Article 40 of the Constitution of People's Republic of China (PRC). China 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.