Abstract: Metal magnetic memory testing technology is a new method of nondestructive testing technology which can accurately judge the location of stress concentration of components and evaluate the degree of fatigue damage, and the magnetic memory signal cannot deviate from the environmental magnetic field. In order to discuss the specific influence of environmental magnetic field on the magnetic memory signal, a static load tensile test on 45 steel was carried out under different environmental magnetic field, and the magnetic memory signals under different stress with same magnetic field were measured. The result shows that environmental magnetic field cannot change the shape of magnetic memory signal curve, but can change the size of the value of magnetic memory signal. In a certain range of magnetic field, the value of magnetic memory signal increases with the increase of the environmental magnetic field, but the value of magnetic memory signal decreases when the environmental magnetic field exceeds a certain threshold value. When the environmental magnetic field is zero or completely offset, stress cannot produce magnetic memory signals. Therefore, the impact of environmental magnetic field must be considered in the magnetic memory testing practice, especially in the quantitative detection applications.