In the paper,according to the characters of the target imaging by laser with “cat eye effect”,an effective anti-jamming detection algorithm is put forward,through which,the target around 1000 meters is successfully detected.In the algorithm,a new rotundity character parameter——linear eccentricity is defined.Comparison between the new parameter and the usual parameter eccentricity is discussed.Experiments results prove that the new parameter is more accurate to distinguish round shapes.