Two nucleon stripping reactions are formulated in a convenient form for the DWBA calculation based on the direct interaction mechanism. The cross section is written as a product of two factors, one is the spectroscopic factor which reflects the nature of the nuclear structure concerned and the other is the one body transition matrix element. The latter factor describes the process in which the target nucleus captures two nucleons as a cluster into an orbit which is characterized by a form factor. This method is applied to the interpretation of the experimental results by Harvey et al. and also comparisons are made with experiments of Ca40 (d, α) K38 reaction.