In　this　paper,　the　optical　gain　characteristics　and　optical　high　frequency　characteristics　of　an　InP-based　uni-traveling-carrier　double　heterojunction　phototransistor　(UTC-DHPT)　are　illustrated.　The　detailed　analysis　of　UTC　effects　on　those　perfomaces　show　that　UTC　transport　mechanism　successfully　weaks　the　space　charge　effect　in　the　collector　junction　and　breaks　the　limitation　of　low　mobility　of　the　holes.　Compared　with　traditional　single　heterojunction　phototransistor　(SHPT),　UTC-DHPT　improves　its　processing　ability　of　high　power　optical　signal　and　provides　high　saturation　current,　high　responsivity　and　high　response　speed　simultaneoursly.