NOVELTY - The present invention provides a system for adjusting speed of treadmill running belt based on difference of current load. It is provided for precisely reflecting the running speed of the user and adjusting the rotating speed of the running belt of the treadmill correspondingly to be in consistence with the running speed. Thereby allowing the user to stably run on the running belt, and achieve the function of effective exercise management by using current load as an operating factor in combination with various kinds of expression. It improves the conventional structure that adjusts the speed of the running belt of the treadmill to be high or low based on signal transmission generated by physical contact, which is likely to encounter erroneous contact or erroneous determination, resulting in inconsistence between the rotating speed of the running belt and the running speed of the user, and thus being unable to achieve the effect of exercise. Furthermore, an erroneous determination may cause the running belt to rotate too fast, and the user may fall down. The invention connects the treadmill with a control system, or installs the control system on the treadmill. It includes a load sensing detection circuit, a micro-processing unit and a motor driver, in which the motor driver is connected to the driving motor and the running belt is driven by the motor to rotate. The load sensing detection circuit transmits the current loading signal corresponding to user's stepping on the running belt to the micro-processing unit for calculating the time difference between signals. The time difference is compared with the stability difference previously detected. The difference between the latest difference and the stability difference makes the micro-processing unit transmit a signal to the motor driver to enable the motor to drive the running belt to rotate faster, rotate slower, or maintain in a constant speed. When a user use this treadmill to exercise, he is able to suitably adjust the running speed based on his physical capability. Thereby achieving the effect of body-building, and further preventing the user form falling down carelessly due to the difference between the user's running speed and the rotating speed of the running belt. Moreover, with various kinds of formulas built in the micro-processing unit, it is able to provide the user with a better exercise management.