Abstract: In view of problem that nonlinear and impact load inject plenty of reactive power and harmonic wave into coal mine power grid, the paper researched chain circuit STATCOM based on CPS-SPWM modulation. It introduced main circuit structure of chain circuit STATCOM; for two modulations of unipolar CPS-SPWM and bipolar CPS-SPWM in chain circuit STATCOM, it used Matlab to analyze differences between unipolar CPS-SPWM modulation and bipolar CPS-SPWM modulation based on H-bridge basic module and cascade H-bridge, the simulation result showed that waveform quality of unipolar CPS-SPWM modulation is superior to one of bipolar CPS-SPWM modulation, so chain circuit STATCOM should select unipolar CPS-SPWM modulation; it used Matlab/Simulink platform to make simulation for chain circuit STATCOM based on unipolar CPS-SPWM modulation under different modulation ratios, the simulation result showed that the chain circuit STATCOM has characteristics of good output waveform, low harmonics and strong expandability.