A valveless piezoelectric pump with variable cross section Y-shape tubes is developed based on the structure of the three-way diffuser／nozzle tube. Firstly, the working principle of valveless piezoelectric pump with variable cross section Y-shape tubes is analyzed. Then, the theoretical analysis is applied on pressure loss coefficient of the variable cross section Y-shape tube and flow rate of the pump. Meanwhile, the commercial finite element software CFX is employed to simulate the flow filed of the tube to obtain pressure loss coefficient along positive and negative direction of the tube. Finally, this valveless piezoelectric pump is fabricated, and the relationship between the flow rate and driving frequency, as well as the relationship between the flow rate and the driving voltage are experimentally investigated. The experimental results show that the maximum flow rate is 25.7 mL/min with driving frequency 12.4 Hz (100 V), and the maximum flow is 41.6 mL/min under 200 V (12.4 Hz) power supply. The experimental results validate the feasibility of the valveless piezoelectric pump with variable cross section Y-shape tubes.