Abstract: The existing semi-coke has the advantages of high fixed carbon, low ash, low sulfur and low phosphorus, but it has low volatile and slow ignition. Adding a small amount of biomass into the semi-coke fuel can effectively improve its combustion performance, reduce the emission of coal-fired pollutants, and optimize the utilization status of biomass straw. In this paper, the combustion characteristics of three kinds of semi-coke, wheat straw and corn stalk alone and mixed fuels were studied by thermogravimetric analysis. The effects of the types of mixed samples and mixing ratio on the ignition temperature, burnout temperature, combustion characteristic index and heat release rate of mixed fuels were analyzed. The optimal mixing ratio was determined. The results show that the combustion effect of the mixed fuel is closely related to the type and proportion of the mixed fuel. The combustion properties of the five samples are wheat stalk, corn stalk, Fugu semi-coke(SC1),Datong semi-coke(SC3) and Inner Mongolia semi-coke(SC2),in descending order. The combustion properties of SC1 mixed with corn stalk are better than those of other mixed fuels. Compared with the original sample, the ignition temperature and burnout temperature of the fuel are reduced by about 200 ℃ and 40 ℃,respectively, and the comprehensive combustion characteristic index is about 1.5 times of the original sample. When the mixing ratio of SC1/straw is 8∶2,the ignition characteristic index is only 0.625,which is lower than the original sample′s ignition characteristic index(0.979). The actual value of the first wave peak is also less than the theoretical simulation value. The mixed fuel has inhibitory effect on the volatilization analysis of straw in the low temperature section. With the increase of the straw mixing ratio, the promoting effect is greater than the inhibiting effect. The first wave peak migrates and increases, while the second wave peak decreases. When the mixing ratio is 6∶4,there is a brief increase at the second wave peak. It is possible that the increase in the proportion of straw and the cracking of a large amount of flammable semi-coke results in the acceleration of combustion in a short time. Mixing a certain proportion of straw in the semi-coke is beneficial to reduce the activation energy of the fuel in the main combustion stage, but the improvement of combustion performance is limited with the increase of the mixing proportion. When the mixing ratio of SC1 and corn stover is 6∶4,the activation energy of SC1 is reduced by 36 kJ/mol. When the mixing ratio of SC1 and corn straw is 7∶3,the heat release rate of the blended fuel is significantly higher than that of other blended fuels. Combined with its combustion characteristics, it can be found that the fuel with this mixture ratio has the best combustion effect.