Abstract: This paper analyzed the harm that reactive and harmonic current brought to the coal-powered system,and devised a set of reactive power compensation device based on STATCOM.By the traditional method of compensation current detection on instantaneous power,this paper proposed p-q detection based on voltage detector of positive sequence.It could measure harmonic and reactive component of the load in the conditions of power grid imbalanced or distorted quickly and accurately.Using hysteresis comparison control for current tracking can effectively solve the complex problem of the power supply system.