Conventionally, piezo-electric inkjet devices have been computationally simulated in two separate areas: a structure analysis of a piezoelectric actuator and a body forming flow channels and a fluid flow analysis. Individually, their results showed fair accuracy. However, the challenge of the simulations lies on making the connection between the analyses.A new approach of combining the two different analyses is described in this paper. First, we used the conventional lumped model for an ink-jet device system except the meniscus movement in the orifice. The lumped model was divided into several components, described with simple mechanical elements. The applied electrical voltage was replaced with equivalent normal stresses on the actuator, and so the structural analysis includes the deflection of an actuator in the modeled mechanical system. Second, three-dimensional fluid analysis was implemented for the flow around the meniscus, predicting the characteristics of droplet dynamics. In order to combine their results, two analyses were set to share variables at the boundaries - the inlet velocity of the orifice and the pressure of fluid under the meniscus. The simulation results successfully predicted the dynamic response of the system and drop ejection phenomena, such as the velocity and size of droplet. To predict the optimal structure and driving signal, the results of the simulation were compared with those of the experiment in the parameter study