A measuring system for analyzing a knee joint motion trajectory when a rider is riding a bike (cycling) and a measuring method thereof are disclosed. The measuring system includes a pedal-able device, a light emitting component fixed at a tibial plateau of the rider, an image capturing device, and a knee joint motion trajectory analysis device. When the rider continuously pedals the pedal-able device, the image capturing device captures an image of a central position of the riders lower limb and a light spot trajectory image of the light emitting component. The motion trajectory analysis device generates an ellipse motion trajectory diagram. After comparing and analyzing a body central line with a trajectory long axis line, a foot force distribution and a shifting data of the knee joint motion trajectory is acquired, and a proper insole is determined.
