A safety ensuring system of exercise machine and a related method includes a physiological detection device and an exercise machine. The physiological detection device is used to detect a physiological state of a human body and save the physiological state. Before a user using the exercise machine, the physiological state of the user is detected by the physiological detection device first. The exercise machine includes a control device and a working device, wherein the control device determines whether the working device is allowed to be used according to the physiological state saved in the physiological detection device. The working device is allowed to be used if the physiological state is normal, and it is prohibited from being used otherwise. Whereby, the user in poor physiological state is prevented from doing exercise, which effectively ensures the safety at using the exercise machine.