Based on the national standard GB 5009.4—2016, the relative contribution of each influencing factor to ash content change of wheat flour was studied, including sample weight, carbonization time, ashing time and ashing temperature. All the data were analyzed by Grubbs’test method. Ash content results indicated that the recommended weight for wheat flour is 3 g. Carbonization time and period were very important. The recommend means of ash temperature and ash time for wheat flour samples were 550 ℃ and 4 h, respectively. Means of ash content between dry basis and wet basis varied slightly. Finally, a measurement was proposed for wheat flour ash content based on the new standard of GB5009.4—2016.