Embodiments of the present disclosure provide a time service method, a terminal device, and a network device. The method includes: determining, by a terminal device, a first moment of a first downlink message, and determining a second moment of the first downlink message; determining, by the terminal device, a third moment of a first uplink message, and determining a fourth moment of the first uplink message; and determining, by the terminal device, a time offset between the terminal device and the network device based on the first moment, the second moment, the third moment, and the fourth moment. According to the method provided, a time service error is effectively reduced.