Photodetector plays an important role in the optical phased array radar.Lacking of high-power and high-speed optical detector is the bottleneck that restricts the practical application of the optical phased array radar.The direction coupled photo diode,that has been put forward recent years,can solve the problem of uneven distribution of photocurrent under the super mode matching condition.As a result,the new photodetector must be able to work at high-power and high-speed.In this paper,based on the structure of vertical direction coupled waveguide detector,we determine the structural parameters which meet the super mode matching condition by using the simulation results of Beemprop software.In addition,using the effective index method,we verify that the structural parameters still meets the super mode matching condition.The method used in this paper provides a reference for the design of high-power and high-speed photodetector.