Systematic studies on the structure of defects in InP caused by electron irradiation are conducted basing on the experimental measurements and theoratical calculations. The introducing rates and annealing out temperatures of In and P vacancies are estimated using proper theoratical models. These calculations reveal that after room temperature irradiation only complexes may exist. It is also supported by our experimental data that the sum of introducing rates of three detected levels are less than the theoratical value calculated for single vacancies.According to our equation on the relation between interface states and DLTS signal and result of computer calculation we believe that the broad peak appeared in DLTS diagram before irradiation is related to interface states. Its disappearance after electron irradiation suggests the reduction of interface state, this is further comfirmed by the reduction of surface recombination rate derived from the result of surface photo voltage measurement.