In order to realize the automatic image registration for infrared images and visible images, an image registration method based on the Expectation Maximum(EM) iteration of the log-likelihood function is proposed. This method utilizes the image edge as the registration point, and thus the image registration is transferred into an edge point set registration. The point set is modeled as Gauss Mixture Model (GMM), and the likelihood function of the point set registration is obtained. To solve the affine transform parameter, the likelihood function is maximized with EM iterations. And during the EM iterations, the probability density of edge point is segmented with an adaptive threshold to eliminate the outer points, and the interference of outer point with the likelihood function is overcome and the affine transform parameter is determined accurately. The experiments on image registration for infrared images and visible images are verified,and the results indicate that the proposed method is effective.