Using behavioral models to perform system simulation at behavioral level is currently a popular solution to verify SOC designs. For analog behavioral models, most of previous approaches are developed with the assumption that noise waveforms are known functions, such as sinusoid waves or Gaussian noise. However, while co-simulated with other blocks in the system, the actual supply noise induced by other circuits is often very irregular and unpredictable. Therefore, the simulation results may still have some errors in real environment. In this paper, an efficient behavioral modeling approach for PLL designs is proposed to analyze the real-time supply noise effects. Instead of directly modeling the final circuit performance as a single complicated equation, we try to model suitable intermediate parameters whose relationship to supply noise is much simpler. The experimental results have shown that our approach can accurately deal with irregular noise with such a simple model.