To enhance the edge response of the image and then extract the edge robustly,a pre-processing method based on inverse bilateral filtering is proposed,which will make the edge appear perfectly.For bilateral filter having good capability to preserve the edge and good response on low and high frequencies,a new concept for inverse bilateral filter is constructed.And then,strategies of self-adaptive threshold and non-maximum suppress are adopted to extract the edge from the gradient module map of enhanced image.Experiments show that the proposed method has better extraction result with variable illuminance and less sensibility to the noise.