Abstract: For giving data sets,this paper gives a method that is how to detect the influential factor.It use the generalized DEA model(based on input model and output model) to study the influence on the inefficient DMU when delecting an efficient DMU in the efficient DMU set.It gives the calculative method about the influence factor.It puts forword the oblique projection model and gives the calculative method.At the end,it is applied to analyse an example.