An important characteristic of shape memory alloy (SMA) is that under the effect of a certain temperature or load, phase changes of this material occur in the solid form. Therefore, during the process of friction when the normal load is great enough, phase transformation locally occurs within the actual contact area, resulting in changes in mechanical properties of the material at the point of contact, thus altering the friction feature. Based on a single point contact Hertz model, the contact model with a steel ball contacting the Ni-Ti flat surface was established. By analyzing the process of plastic deformation induced by the normal load, the influence on the friction process of Ni-Ti SMA by normal load was discussed, and the results were compared with that from experiments. Both of theoretic and experimental results indicate that, when the normal load is small, the friction coefficient is inversely proportional to the normal load, and when the load exceeds a certain value, the friction coefficient is almost unchanged. The research conclusion can be used to predict the friction property of SMA, so as to control and reduce the wear caused losses of the parts.