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A valveless piezoelectric micropump applying Coanda effect has been developed. The dynamic mesh method and numerical simulation were applied for studying the fluid field and performance of micropump. The results show that due to the Coanda jet, the volume efficiency η of the micropump was able to reach over 0.5 at zero pump pressure, which was larger than the traditional diffuser/nozzle valveless micropump. The effect of the flat cone tube and the concaved surface was discussed and the results show that the length of flat cone tube must be larger than dcot(θ/2), and when c2/c1=1,L1/d=9, the flowrate of micropump reaches a maximum at zero pump pressure. And the comparison of η with the different c2/c1 and pump pressures shows the large width of the concaved surface could enhance the performance of micropump at a high pump pressure, but reduce the performance of micropump at a low pump pressure. Response surface methodology was utilized to optimize the structural parameters. When the pump pressure was 5kPa, the recommend region was 4≤L1/d≤5 and 0.75≤c2/c1≤0.85. When L1/d=4.3 and c2/c1=0.80, the maximum volume efficiency was 0.323 and the difference was 1.89% comparing with the value of simulation which was 0.317.