Variance can express the relationship among the pixels in a small area.Generally speaking,the variance of different pixel is different when the area size is same,and the variance of same pixel is different when the area size is different.In this paper,a Multi-scale Variance algorithm is proposed to compute the change of variances resulting from different scale.That change in the target is big and that change in the background is small.Finally,it uses rows and columns projection to find the big change as the target position.The experimental results show that the proposed algorithm is successful to suppress the noise and get the position of infrared warship target.