We have been developing an evaluation method of liver fibrosis using ultrasound images to realize quantitative diagnosis of hepatitis. To evaluate liver fibrosis quantitatively, we have focused on a probability density function of the echo amplitude. Then, a multi-Rayleigh distribution model expressed by combination of Rayleigh distributions with different variances has been proposed. This multi-Rayleigh distribution model enabled us to extract fibrosis parameters from a B-mode image. However, the B-mode image is affected by a resolution of the ultrasound; therefore, the fibrosis parameters estimated from the B-mode images deviate from their true values. In this paper, we examined the effect of the resolution of the ultrasound by computer simulation. As a result, we could see that the estimated fibrosis stage becomes smaller and the estimated amount of the fibrotic tissue becomes a little larger than their true values. Then, we tried to compensate the effect of the resolution. We showed the possibility that we could correct the estimated fibrosis parameters to their true values by considering the relationship between the estimated fibrosis parameters and the resolution size of the ultrasound.