The purpose of this research is to improve the rotation mechanism theory of the SMA engine. The main results obtained by this research are as follows. After having taken the bending moment (occurs when the SMA belt is pulled back) into consideration and having incorporated that into the rotation mechanism theory, we have stepped up to the next level of accuracy. According to our modified theory, we will be able to calculate the predicted values of rotation speed ω and output power P with higher accuracy. We designed and assembled a large-sized equipment which allowed us to measure the rotation speed and the torque simultaneously. We compared the experimental values of the output power with the theoretical values, and partially verified the validity of the theory. We obtained the maximum output power 3.74W.