Piezoelectric inkjet printing technology has wide applications in electronics manufacturing, additive manufacturing, and printing. The fluid channel structure parameters of the printhead are crucial factors affecting droplet ejection. This paper focuses on the bending-type piezoelectric inkjet printhead. Based on the Lumped Element Model (LEM), each component of the printhead is represented by corresponding ideal circuit elements. The coupling of the electrical, mechanical, and fluid energy domains is achieved by connecting all circuit elements into an equivalent circuit, establishing a lumped element model for the piezoelectric inkjet printhead. This study investigates the influence of fluid channel structure parameters on droplet ejection characteristics, with the main parameters being pressure chamber height, nozzle thickness, and flow restrictor width. The optimal structural dimensions for each part of the printhead were determined and validated through simulations. The results show that the lumped element model established in this paper has a short computation time and high accuracy.