A kind of sensitive slippage sensor was developed by using piezoresistor, and a slippage observation system was constructed. The technique of STFT was applied to analyze the spectral information of slippage signal. Then slippage signal was distinguished with the signal resulted from different normal griping forces by using the result of DWT. The experimental results showed that the slippage signal was able to be effectively extracted regardless of different normal gripping force. At last, the experiment of gripping force adjustment was carried out by using two parallel fingers hand equipped with the designed slippage sensor. The experimental results of grasping actual fruits and vegetables demonstrated the promise of this slippage sensor in the agricultural picking robot. 