The invention relates to a constant temperature crystal oscillator-based time synchronization device time-keeping method and a time synchronization device. The method includes the following steps that: when time-keeping is carried out, the actual frequency of a reference frequency provided by a constant temperature crystal oscillator and the number of pulses per second are obtained under the condition of the presence of a synchronous clock source; the sum value of the number of pulses in a set number of seconds is calculated sequentially every set number of seconds, and is recorded as a beta value, and obtained sum values are sequentially stored in a buffer queue; when the synchronous clock source is lost, the obtained beta values are processed correspondingly, so that the frequency compensation value of the constant temperature crystal oscillator is obtained, the change of the frequency of the constant temperature crystal oscillator can be predicted; and time-keeping second pulses aregenerated according to the frequency compensation value, and the time-keeping of the time synchronization device is realized. With the method of the invention adopted, frequency variation caused by the insufficient warm-up of the constant temperature crystal oscillator can be predicted and compensated, subsequent time-keeping errors are reduced, and the time-keeping accuracy of the synchronous clock is improved.