An efficient algorithm was presented to solve the problems of the speed and the staircase effect in the image denoising. In the Bayesian framework, firstly, the harmonic model was introduced as the prior model of the original image, and the Gamma distribution was supposed to be the prior distribution model of the unknown parameters. Secondly, the maximum posteriori probability was deduced using the variational method, based on which the original image and the unknown parameters were estimated simultaneously to remove the noise in the observed image. The experimental results show the efficiency of the proposed algorithm. Furthermore, compared with other similar algorithms, the proposed algorithm shows the competitive performance on the speed without bringing the staircase effect to the denoised images.