The invention discloses a method and a system for detecting different sleep stages of a human body. The method includes the steps: initializing parameters; acquiring human body resistance data; analyzing the human body resistance data; outputting the different sleep stages of the human body and the changeover condition of the sleep stages. Data analysis includes resistance data preprocessing, logarithm taking, window processing, logarithm difference comparison, current human body state value calculation, interval state value calculation and different sleep stage analysis and judgment. The system comprises a medical pole piece, a bridge resistance/conductance measurement circuit, an amplifying circuit, an A/D (analog-to-digital) conversion circuit, a CPU (central processing unit) and a human-computer interaction interface which are sequentially connected. By analyzing the changing rule of human body resistance, the physiological state activity condition of the human body in a sleep period is judged, so that different stages of a testee in the sleep process are quantitatively detected.