The invention discloses a time synchronization method and a time synchronization system based on an NTP network, and relates to a time synchronization method and a time synchronization system. Currently network communication time is compensated through a network, so as to reduce error during timing, but a clock can not be accurate to seconds. The method comprises the following steps: a main station sends a request for inquiring an accurate clock to a terminal; the terminal responds to the request for inquiring an accurate clock of the main station; the main station records the time for receiving the request response and repeats the previous step; the main station computes the time of network transfer from the main station to the terminal, and sends a request for modifying the time deviation to the terminal; the terminal conforms the request and modifies the time; the main station inquires the terminal time; the terminal returns the terminal time to the main station; the main station conforms the correctness of the terminal time, and then sends a timing request to the terminal; the terminal performs time synchronization on a primary meter according to the timing request of the main station; the terminal conforms the time synchronization. The technical scheme improves the time synchronization precision, obtains the accurate occurrence time of instantaneous data, such as load, voltage, current and the like, and improves the correctness of time-of-use electricity price computation.