The detection method of mixed format RMB banknote based on position is put forward.A pair of photoelectrical position sensors and a pair of countors are used in currency count machines.The mixed format banknotes mixed in batch RMB 100 yuans are detected.Two piece of other format banknotes are mixed in one hundred 100 yuan RMB banknotes,if they are counted 100 times,the times of mixed format leakage detection is no more than 1.