Abstract: With the increasing number of distributed generation connecting to the distribution network, the network structure is becoming more and more complex. the network also becomes more flexible to operation, power quality problems in distribution network is becoming more and more complicated situation, voltage and current distortion is serious. In this paper an improved detection algorithm based on instantaneous reactive power theory is presented, this algorithm which is based on i_p-i_q method can detect the reactive power and negative sequence compensation of random harmonic current respectively in real time. The series structure of PI controller and repetitive controller is used to control the harmonics to produce an current injection line that is equal in magnitude and opposite in direction, so that the current in the line tends to be sinusoidal to cancel the harmonic and reactive influences. The effectiveness of the proposed method is verified by the prototype experiment.