The invention provides a method for controlling harmonics of a UPQC (unified power quality conditioner) containing a photovoltaic power distribution network. The method is implemented by the UPQC, and the UPQC comprises a signal collection module, a signal conditioning module, a microcontroller and a driving circuit module. The method comprises the following steps of 1, collecting of a voltage signal: collecting three-phase bus voltages (ua, ub and uc) and load currents (ia, ib and ic) of the power distribution network; 2, conditioning the collected signal; 3, calculating a harmonic compensation instruction; 4, using a self-adaptive linear neural network to set the PI (proportional integral) control parameters (kp and ki) of the UPQC; 5, using the selected optimum PI control parameters (kp and ki) to implement PI control, and outputting current harmonic compensation components. The method has the advantages that by adopting a PI control method for setting the PI control parameters based on the self-adaptive linear neural network, the harmonics containing the photovoltaic power distribution network can be effectively controlled; a new method is provided for using the UPQC to control the power quality of the power distribution network.