The digital speckle correlation method based on bivariate quadratic polynomial curved surface fitting method for precise sub-pixel localization has the advantages of simple calculation and high efficiency. The original method usually selects nine pixels around the integer pixel for surface fitting. We use the nearest six pixels around the integer pixel and the correlation coefficient to directly solve the bivariate quadratic polynomial through analyzing the possible improvement schemes of surface fitting. The speckle patterns are generated by computer simulation, as well as the rigid body translation experiments and uniaxial tension experiments are simulated respectively. Experimental results show that the improved scheme has the advantages of high computational efficiency and small computational error.