An efficient algorithm was proposed to correct the image distortion caused by a resonant scanner in higher speed scanning and imaging systems of confocal or two-photon laser scanning microscopes. A model of scanning movement for the resonant scanner was established, the movement formula of the nonlinear scanning was deduced, so that the distortion equation of the image was obtained. Then, a Ronchi grating sample was imaged by canning, the multi peak Gauss fitting algorithm was designed to get all grating line widths. Those unequal line-widths were fitted into a distortion curve by least square method. Finally, the image correction was achieved through compressing or streching original image based on correction coefficients from the distortion curve. Experimental results indicate that the curve fitting correction algorithm reduces the maximum distortion and the relative distortion to 1/3 and 1/5 those of traditional one and the correction effect is twice as much as that of sinusodal correction method. The fitting correction algorithm does not need to add other light paths and segment edge images, so it shows good image efficiency and correction effect.