A system and a method related to data fusing are provided. The first and second sensing data are obtained. The data combination is determined based on the first and second sensing data. The third sensing data is obtained based on images. Whether the human body portion exists in the third sensing data is determined during the first duration. The motion information is determined by a first determining factor, which includes the data combination and the third sensing data of the first duration, in response to the human body portion existing in the third sensing data. The motion information is determined by a second determining factor, which includes the data combination and the third sensing data of the second duration, in response to the human body portion not existing in the third sensing data. The human body portions of the user exist in the third sensing data during the second duration.