A motion estimation system comprises: an initializing module generating a first initial motion field by allocating an initial motion vector to each block of a first motion field related to a first motion change of an image which accompanies a change from an (n−1)-th frame to an n-th frame and generating a second initial motion field allocating an initial motion vector to each block of a second motion field related to a second motion change of the image which accompanies a change from the n-th frame to the (n−1)-th frame; and a candidate test module generating first and second random motion fields based on a similarity function and each block of each of the first and second initial motion fields and random motion vectors, generating first and second spatial propagation motion fields based on the similarity function, and generating first and second optimum motion fields based on the similarity function.