Circumferential micro-turbine adapts to miniaturization as it has simple structure. To evaluate and improve the six-blade micro-turbine structure and analyze the influence of tip clearance on the flow, To simulate the output characteristics and gas flow characteristics, a three-dimensional transient numerical simulation model is set up and the output characteristics and gas flow characteristics are simulated. Results show that the six-blade turbine has structural defect. Parts of gas directly exhaust without working because intake port and exhaust have periodic connectivity while running. Simulation results for the improved eight-blade micro-turbine reveal that it hasnt such defects. Then, the effect to pressure drop of tip gap is simulated, and results show that the influence is nonlinear. As the gap is less than 0.01, the pressure drop is very sensitive to the gap. When gap is greater than 0.02, its impact is very small. Simulation and experimental results both show that the output mechanical power of the eight-blade turbine and six-blade turbine increases with the increase of gas flow. The eight-blade turbine mechanical power is 1 355 mW, which is increased 10.5% over the six-blade turbine. The power output start flow of eight-blade turbine is 140 L/h, while that of six-blade turbine is 200L/h. The performance of eight-blade turbine is better than that of six-blade turbine.