In order to achieve the manipulatorps soft grasp function, the key is to have slip sensors with fine performance. Depending on the elastomer and photoelectric elements installed in the hand, the sensor transforms the slippage between the grasped object and the robotps hand to electric signal, thus the slippage can be detected. It will cause elastomerspmicro-vibration when the object is slippage. Based on the vibration theory, dynamic theory, light intensity theory and elastic deformation theory, derived is the conclusion that the objectps slippage acceleration relativing to the robotps hand has linear relationship with the photoelectric elementspoutput voltageps differential, and then the model for slippage distinguishing is set up.