For the problems of low frequency series resonant heating system, such as small power adjustment range, slow frequency rhythm and hardware complex in the process, AC/DC/DC/AC topology is used in this paper. In this construction, based on DSP zero-crossing capture and SPWM combined, to detect whether the voltage and current in the same phase or not；according to the size of the phase difference step-by-step control, speed adjustment, reduce the shock, to control the induction heating system work in the resonant state; and increase the temperature adjustment range through adjusting the SPWM modulation degree; not only the influence of current zero - crossing detection circuit on phase lag is analyzed, and an improved method is proposed, but also TMS320F28335 and so on are used to construct example circuits and verified the control algorithm. In conclusion, the experimental results show the feasibility of the selected circuit and control strategy.