Experimental verification and theoretical analysis on the one mirror inclined three mirror cavity (OMITMC) photodetectors in our laboratory is reported.Such kind of photodetectors is newly proposed and very promising of high performance.In the structure of the photodetectors,it is the inclined mirror that makes the filtering cavity and the absorption cavity decoupled,thus narrow spectral response linewidth,high speed and high quantum efficiency can be achieved simultaneously.On the basis of theoretical analysis,the experimental verification on the principle is performed with separated optical components.