Abstract: The improved micro diffuser was suggested in the design of a 6cm-diameter micro turbine engine MJ-S1. The improved micro diffuser,which is composed of the full blades and splitters in the passage rear,can avoid significant mixing of airflow and air velocity of annular turning bend while reducing Mach number losses. The design method of the improved diffuser was put forward in this paper. The effects of passage area and blade angle on the diffuser characteristic were studied by using the computation fluid dynamic code NAPA. The diffuser has higher performance when the passage area distribution is convex and the blade angle is nearly linear. The calculation results show that the total pressure recovery coefficient of the improved diffuser can approach 0.9,when it is operated in the centrifugal compressor stage.