To improve the efficiency of the determination of the crude protein ingrain and oil seeds, and reduce pollution of the ecological environment caused by reagent consumption, taking wheat, corn, sesame, and peanut as samples, the optimal condition by Dumas combustion method was determined after optimizing the testing parameters, such as sample volume, oxygen flux and oxygen factor. The optimal testing condition was: the temperature of combustion tube 990℃, the temperature of reduction tube 650℃,sample volume 100～180mg, oxygen flux 300mL/min and oxygen factor 1.3～1.6mL/mg. The recovery experiment showed that when EDTA was 80mg, the recovery ratios of the four samples were 99.21%, 100.54%, 99.49% and 99.10% respectively. Compared with Kjeldahl determination, there was no significant difference between the results of the two methods. Dumas combustion method is accurate and reliable attested by both addition test and contrast test, which can replace Kjeldahl determination for the determination of crude protein content ingrain and oil seeds.