The knee joint is the largest joint in the human body. It is an essential component responsible for human locomotion, and extremely vulnerable to injuries. In order to enhance the knowledge of the colleagues of the physical therapists, this paper reviewed many literatures related to the knee biomechanics and their clinical significance. From the biomechanics point of view, this paper reported the mechanical function, the range of motion and the loadings of the knee joint. In the end, several examples were proposed to demonstrate the biomechanical approaches in the clinical studies. Hopefully, this paper can provide physical therapist some insight to make proper choice of the clinical treatment.