Sitting posture comfort is a complex construct influenced by several factors. There is no established assessment method which could evaluate the sitting chair comfort at present. Most of the current evaluation methods are based on single analysis, and lack multianalysis of the problem. This paper proposed a new method which integrates investigation methods in real environment and virtual environment. Firstly, Motion Analysis Eagle Digital System was used to capture the body motion of participants, and obtain the human body each joint point in the space. Then, the Motion Analysis EVaRT software was connected with the Siemens Jack software. Using the JACK software TAT report tools to output data, the analysis of data was completed using a selfdeveloped program in MATLAB. After analyzing all the results of motion study, a clear difference between the two types of chair became apparent. The joint angles, torques and muscle force were calculated. Meanwhile, we studied the muscle comfort index to explore new method that evaluates the sitting posture comfort index. The sitting posture comfort index method combined with the human body digital model can analyze the siting posture comfort. Also, this research can be applied to optimize comfort level of the body sitting posture.