N doped ZnO thin films were prepared by magnetron sputtering. The effect of bias voltage, N2 flow and introducing of Al on the behavior of N doping into ZnO films were investigated. The results show that there is little help for N doping into the ZnO films by just adjusting N flow rate because the magnetron sputtering method has a relative weak ability on dissociating the N2. The data of co-doping of Al and N into ZnO films revealed that co-doping is an effective way to advance the N doping into ZnO films. The coordination of Al doping and bias voltage could help the N doping effectively.