In response to the serious problem of backflow in valveless piezoelectric pumps, this paper proposes a valveless piezoelectric pump with a bullhorn-shaped structure. In this paper, we analyze the flow guide by using the "tail flow space pressure comparison method" and "fluid unit dynamic analysis method," revealing the working principle of the flow guide in the valveless piezoelectric pump. The effects of the height, sharp angle, and filter angle of the bullhorn-shaped structure on the output flow were investigated separately by the experiment. The experimental results show that the output flow rate is best when the height of the bullhorn structure is 2 mm, the choke of the bullhorn-shaped structure is 2, and the sharp angle and fillet angle are 180°. The output flow rate of this valveless piezoelectric pump can reach 170.6 ml/min at a drive voltage of 210 V and a drive frequency of 45 Hz, indicating that the valveless piezoelectric pump has good pumping capability and can effectively alleviate the backflow phenomenon. This study offers some valuable insights into improving its performance and practical application.