A modem includes a temperature detecting module, a frequency detecting module, and a power offset calculating module. The temperature detecting module detects a real-time-work temperature of the modem. The frequency detecting module obtains a real-time-work frequency of the modem. The power offset calculating module calculates a power offset by inputting the real-time-work temperature and the real-time-work frequency into a pre-stored calculating model and adjusts a power of the modem according to the calculated power offset. A method of adjusting power of the modem is also provided.