In this paper, a behavior modeling method of a buck converter with adaptive voltage positioning (AVP) and PCB parasitics for power distribution network design (PDN) is introduced. The behavior model of voltage regulator module (VRM) is previously proposed for the power integrity modeling and analysis. The proposed behavior model is applied to the buck VRM in a practical high-speed digital board. For the completeness of the behavior model, an AVP design and PCB parasitics are applied to reproduce the power supply rail noise in the practical design. To validate the behavior model, the design parameters of voltage and current controllers of buck VRM in the board are extracted based on the measurement. The proposed model shows a good correlation with the measurement under various loading conditions.