In order to extract the star effectively, and improve the star map identification efficiency and the attitude precision of star map, a method of star extraction based on the commonness between star and small target using morphological was proposed. Background was estimated by morphological and suppressed by gray-scale morphology Top-Hat transform, and the star image was comprised of star target and high frequency noise. Self-adaptive threshold value method was adopted to determine the actual image threshold. The results indicate that the method can well suppress the background noise, and redound to selecting threshold and confirming the brightness of target. Moreover, the brightness of target confirmed is more effective than conventional methods, and the coordinates of centroid compared with the true value does not exceed 0.3 pixels unit.