In order to improve the product quality of compound fertilizer manufacturers in the surrounding areas of Beijing and improve their ex-factory inspection ability，a study is carried out to verify the ability of the manufacturers to determine the total nitrogen content of compound fertilizer.The samples of capability verification meet the requirements of uniformity and stability，and the results of total nitrogen content determination are analyzed by frequency distribution statistics and robust Z-score statistics.The results show that the data of 18 participating capability verification units are distributed in the vicinity of the median value of 17.12，with only a low frequency deviation.The frequency distribution of the measured results is approximately normal.The satisfactory rate of the Z-score judgment is 83.3%，indicating that more than 80% of the compound fertilizer manufacturers’ inspection ability for the determination of total nitrogen content in the compound fertilizer conforms to the national standard GB/T 8573-2010 for ‘Determination of Total Nitrogen Content for Compound Fertilizers Titrimetric Method after Distillation’.Nearly 20% of the compound fertilizer manufacturers still have shortcomings in quality control，so the enterprises should improve the inspection ability and professional technical level of the inspectors，and finally achieve the goal of improving the quality of the products.