In daily life and work, family and work security, unit files, financial statements, and some personal data are mostly kept in a locked way. The coded lock consists of five parts: cryptographic setting circuit, transmitting circuit, decoding circuit, display circuit and power supply circuit. In the coded lock, by inputting the correct password, the NE555 circuit can work normally. After decoding by the decoding circuit, the electric relay closes and the LED lightens; if the password is incorrect, the LED cannot shine. This design can achieve the safety prevention well.