Aiming at the disadvantage of low precision, low efficiency and easily pulled off of the crossflow fan by manual dynamic balance, the NC drilling technology was firstly introduced into this field, and the automatic dynamic balance of crossflow fan by NC drilling was developed by our independent research. First, the mechanisms of dynamic balance and two endface equivalent balance were introduced. Then, the accurately modeling of crossflow fan unbalance by NC drilling was proposed. In the same time, four piezoelectric sensors were used as the measuring equipment of fixed blade support balancing machine, and the analog voltage (0~10 V) of the double emendation plates X and Y direction was output. After that, by signal processing, the analog voltage was transferred to the microcomputer control system by the PCL812PG data acquisition card. And then later, the unbalances of two emendation plate were calculated by the coefficient of analog voltage and unbalance. Finally, the automatic dynamic balance of crossflow fan was came true by NC drilling. The experimental result shows that the maximumachievablereduction ratio of this dynamic balance system can reach up to 90%.