Aiming at the phase difference extraction in speckle pattern interferometry,a novel method is proposed based on the four-step phase shifting. In this method,by collecting the four interferometric patterns respectively before and after the object deforming,a novel mathematical expression of the phase difference is theoretically derived,which avoids the high-frequency noise and the false wrapped phase difference of the general four-step phase-shifting method. The proposed method is then tested by using a circumferentially-fixed disk model with a point loading at the centre and is compared with the general four-step phase-shifting method. The results show that the proposed method is significantly superior to the general one in terms of high-frequency noise elimination and image quality improvement,and that it can not only suppress the noise but also maintain the stripe features.