The paper introduced microstructure, transition mechanism, shape memory effect of ferromagnetic NiMnGa system, and systematically examined external characteristic of NiMnGa magnetic shape memory alloy. The static relationships of magnetic field, temperature, pre-pressure, strain of NiMnGa were obtained. After drawing the dynamic curves of different temperature and pre-pressure, the characteristic features of NiMnGa dynamic strain and static strain were given. The experimental results confirm that with the increase of magnetic field and decrease of pre-pressure, the strain inerease. When the temperature close to austensite temperature, the strain is the largest. Therefore, the results provide a theoretical and experimental basis for practical application of NiMnGa alloy.