With such advantages as low loss，fast dynamic response，small size and low harmonic content，the H-bridge cascaded synchronous compensator（STATCOM）has become an important development direction of the dynamic reactive power compensation equipment.In this paper，the dead-beat control algorithm is deduced via an analysis of the working principle and mathematical model for the STATCOM.To improve the real-time character of the dead-beat control algorithm，eliminate the influence of the reference voltage lag by one beat and reduce the current harmonic content of the STATCOM，a discrete state observer is constructed which can be used to predict the value of the reference command current.To avoid the error of the STATCOM actual output voltage which can be calculated by the dc side reference voltage of capacitance，the discrete sliding form observer is constructed which can be used to observe the actual output voltage of the STATCOM.Simulation and experimental results show that the algorithm can accurately predict the value of reference command current to improve the dead-beat control performance of the STATCOM.