A method based on partial phase synchronization was employed which can distinguish the direct coupling and indirect coupling effectively in a multivariate nonlinear system compared to the bivariate phase synchronization. Applying this method to three coupled stochastic Rossler oscillators, the result reveals that the analysis of partial phase synchronization can infer the correct interactions among oscillators. Using the method to analyze the teenage EEG and middle-aged EEG, the result shows that the coupling degrees of teenage EEG and middle-aged EEG are significantly different. The method of partial phase synchronization can be a reference to distinguish teenage and middle-age EEGs.