The invention discloses a transformer magnetic density control method for a series resonant full bridge converter. The method comprises the following steps of: controlling phase shift between a firstswitch Q1 and a third switch Q3 to be half a switching period 0.5Ts; duty cycles of the first switch Q1 and the third switch Q3 are the same and are half a series resonant period 0.5Tr; controlling asecond switch Q2 to lead a fourth switch Q4 by half the switching period 0.5Ts, and the two switches turn on and off two times in one switching cycle; controlling a first turn-on starting point of thesecond switch Q2 to lag a first turn-on starting point of the first switch Q1 by half the series resonant period 0.5Tr, and turning on only half the series resonant period 0.5Tr; and controlling a second turn-on starting point of the second switch Q2 to lag a second turn-on starting point of the first switch Q1 by half the switching period 0.5Ts, and an on-time should be greater than 0.5Tr but less than one series resonant period Tr. Magnitude of converter transmission power is controlled by varying switching frequency. Under the same output voltage condition, the maximum values of excitationcurrent and magnetic density of the transformer is not influenced by the switching frequency and power variation, and the problem that the transformer is easy to saturate under a light load is solved.