Abstract 【Aim】 A large quantities of crop straws produced annually are not effectively used, causing waste of resources. Some crop straws are fermented into animal feed, but they are rarely adapted as feed of insects. This study aims to extend the utilization of crop straw and to reduce the feed cost for breeding Tenebrio molitor. 【Methods】 Different feed formulas made from the conventional feed of T. molitor, fermented corn stalk and fermented sweet potato straw were designed by extreme vertex mixing design method, and the optimal feed formulation was screened by determining the effects of the feed formulation on the growth indexes (biomass increment rate, mortality, body length, feed utilization rate and conversion rate) and physiological indexes (moisture content, ash content, crude fat content, crude protein content, SOD activity, total sugar content, phosphorus content, content of medium and trace elements, and heavy metal content). 【Results】 The results showed that a certain amount of fermented corn stalk and fermented sweet potato straw added in the conventional feed was more beneficial to the growth of T. molitor. In the experimental groups with higher biomass increment rate, T. molitor had higher feed utilization rates and conversion rates. The higher the proportion of sweet potato straw in the formula, the higher the mortality trend of T. molitor. Different feed formulation had no obvious effect on the body length and physiological indexes of T. molitor larvae. The optimal feed formulation for T. molitor was as follows: conventional feed∶fermented corn stalk∶fermented sweet potato straw=37.24∶20.72∶42.04. Compared with the conventional feed formulation, the feed cost of the optimal feed formulation was decreased by 56.94%. The biomass increment rate of T. molitor larvae reared with the optimal feed formulation reached 32.52%, higher than that reared with the conventional feed (25.17%). Moreover, the mortality rate of T. molitor larvae reared with the optimal feed formulation was low and the utilization of crop straw feed was high. 【Conclusion】 Based on a reasonable formulation, the crop straw can be used as the feed of T. molitor, which can not only reduce the feed cost for breeding T. molitor, but also raise the utilization rate of crop straw. So the formulation is of great application prospective.