The present invention relates to a trench type semiconductor power device and a preparation method thereof. The trench type semiconductor power device includes a first conductivity type base region; acell region is of a trenched structure; cell trenches are disposed in the first conductivity type base region; trench gate structures are disposed in the cell trenches; a second conductivity type floating layer is disposed outside the trench bottom of each cell trench, wherein the second conductivity type floating layer wraps the trench bottom of the corresponding cell trench; a first conductivity type floating layer is disposed at outer side of the lower portion of each cell trench, wherein the first conductivity type floating layer is located in the first conductivity type base region and wraps the corresponding second conductivity type floating layer and the lower portion of the corresponding cell trench; and the second conductivity type floating layer is adjacent to the correspondingfirst conductivity type floating layer and the outer wall of the trench bottom of the corresponding cell trench. With a smaller cell size realized, the trench type semiconductor power device of the present invention has better breakdown characteristic, a forward conduction characteristic and a wide short-circuiting safe working area, and is compatible with existing semiconductor processes.