To achieve the detection and control of the high-power transient synthetic power supply, this paper investigates the controlling method of the power supply and a controlling system including a data acquisition card, a DSP board and a PC is designed. The controlling system consist of a controlling module and a monitoring module. The monitoring module monitor the charging current, the charging voltage, the power frequency steady-state current, the DC transient current and the decaying time. The controlling module is composed of a power frequency power controlling system and a DC power controlling system, while the former implement the function of the control of power frequency current and reactive-compensation unit, the latter control the charging current, the triggering time, the phase-selection closing and the time constant. To synchronize the current in the power frequency loop and in the DC loop, an algorithm is proposed based on bilinear transformation IIR filter and cubic spline interpolation algorithm. The testing results show that the presented controlling system exhibits the characteristic such as safety, reliability, high –speed of processing of data, and accurate triggering, which meets the requirements of the control of the synthetic power supply.