In medical activities，both doctors and patients hold certain psychological state in their communication，due to their different personality traits. These psychological states have a direct impact on the quality of communication between doctors and patients. Based on the PAC theory，this paper discussed the expression characteristics of different psychological states（parent ego state，adult ego state，and child ego state）in communication，as well as the impact of these psychological states on the effectiveness of medical activities. Furthermore，the optimal interaction patterns in doctor-patient relationship are put forward in this paper——“AA-AA” in daily medical service and “PC-CP” in emergency medical service. This paper suggests that hospital manager should train the doctors systematically with PAC theory，strengthen their ability to recognize the PAC ego states，help them improve their psychological state in communication，and encourage them to guide patients to take P ego state. In this way，we can build a trusting，cooperative，harmonious doctor-patient relationship.