In the positioning procedure for point- like sources generated in optoelectronic devices,Cramer-Rao Lower Bound (CRLB) is used to estimate the locating accuracy of the devices contaminated with noise.As the lower bound of any unbiased estimator,CRLB is known as a criterion to assess whether an estimator meets the characteristics of minimum variance unbiased (MVU).The CRLB characteristies on the performance of the imaging device under both Poisson and Gaussian noise are given and accordingly the positioning error of three current centroiding algorithms,center of gravity (COG),iteratively weighted center of gravity (IWCOG) and Gaussian least squares fitting(GLSF),is investigated respectively.Theoretical analysis and simulation results show that IWCOG and GLSF share the same position error and reach CRLB of optoelectronic imaging device,thus meet MVU features.That is to say,COG makes the biggest positioning error,followed by IWCOG and GLSF.And the computing time of IWCOG is just several times longer than COG algorithm,while GLSF algorithm is certainly the time-consuming procedure to make it inapplicable on-board on star tracker.IWCOG is proven to be as a method with low error,real- time and robust algorithm,making it possible for highprecision condition such as star tracker,Shack-Hartmann sensor.