Abstract: The effects of maize roborant and uniconazole on plant height and grain yield of hybrid maize Zhenghong311 were investigated through field experiment in high altitude region of Panxi. The results were as follows: Maize roborant applied at small bell-mouth stage had significant effects of reducing plant height of 12.1%~24.5%, and ear height of 13.5%~16.0% respectively. However, the grain yields were decreased along with 6.7%~8.9% at the same time. It was found that the relationship between plant height and grain yield was quadratic protruding function. As a result, the grain yield is the highest while plant height optimum.