A method and device are provided for encoding a master information block (MIB), where the MIB includes indication information, the indication information is used by a terminal device to determine a decoding mode for decoding first information, and the first information includes at least one of a system information block (SIB) 1 and system information (SI); and sending an encoded MIB to the terminal device. The terminal device can determine a correct decoding mode for the SIB and the SI according to the indication information before receiving the SIB and the SI, and then the terminal device can decode the SIB and the SI in the correct decoding mode after receiving the SIB and the SI. The terminal device can flexibly decode the SIB and the SI.