Abstract: To improve sampling precision of sampling system,the automatic sampling system was transformed and the effects was analyzed through variance analysis. The system had the problems of high failure rate,frequent blockage and large deviation. The transforming measures were that adjusting the position of squeegee gasket and conveying belt roller,improving maintenance frequency,setting the angle of guide plate at feed opening of secondary sampling process to 45°,regulating coal thickness in the middle of conveying belt and speed of conveying belt. After transformation,the total mean square error of system was 0. 313%.