The numerical simulation of shape memory alloy actuators requires the solution of the coupled thermo-mechanical, phase transformation, and constitutive relationship equations. Simulation results are highly affected by parametric values as well as modeling equations. Specifically, the martensite fraction affects the simulation results of the actuator significantly for various input excitation as fraction of martensite is often modeled with a switching function. Depending on the assumed model this may cause changes in other properties of the system. Therefore in this study, we investigate the modeling of NiTi shape memory alloy based on the available phenomenological models and study the effects of integration step, numerical solver parameters and code formulation in Matlab/SIMULINK. To emphasis on the numerical solving procedure a simple spring biased SMA actuator configuration is chosen. Simulation results from multiple available models are provided and discussed.