In this paper, we present simulation of nonlinear oscillation motion behavior from encapsulated ultrasound contrast agents (UCAs) insonified by acoustic pressure from ultrasound wave. The backscattered signals from UCA are composed of fundamental, second harmonic, ultraharmonic and subharmonic frequencies. Especially, the subharmonic generation is specific in UCA region. Then, the subharmonic can provide higher contrast-to-tissue ratio (CTR) than the fundamental and the second harmonics. As a result, the subharmonic components can be effectively applied for medical diagnosis. In this work, we study the optimization of ultrasound parameters, i.e., the transmitted frequencies and acoustic pressures, for subharmonic generation. The results show that the subharmonic generation can be maximized using the transmitted frequencies between 1.5ƒ<inf>r</inf> (resonant frequency) MHz and 2ƒ<inf>r</inf> MHz, and the acoustic pressures values in the range of 0.6 to 1.2 MPa.