The analytical study of the ink-jet head(IJH) may be applied to design IJH efficiently and optimally. This study presents the theoretical approach to design IJH. The mechanical system of IJH is simply designed to electric circuit with inertance, resistance and compliance, IJH that is composed of actuator, chamber, reservoir, restrictor, and nozzle including ink. The voltage and current in the circuit represent the pressure and velocity in the mechanical system, and therefore the size and velocity of the droplet can be calculated easily to design the structure of IJH, the shape of the driving signal and so on. Since there are many kinds of variables such as the material properties of ink and actuator and geometric values of the IJH, the material properties of ink are primarily defined to the values of the commercial ink of the ink-jet printer. The performance of IJH depends on the various factors, but this study concentrates not only on the resistance ratio and inertance ratio between restrictor and nozzle, but also the width of the PZT actuator. These variables have a great influence on the performance. To realize the theoretical approach more accurately, this study shows new methods.