The invention belongs to the field of tobacco cultivation, and specifically relates to a controlling agent for preventing flue-cured tobaccos from being forced to ripen at a high temperature. The controlling agent comprises the following components: polyamine, sodium nitroprusside and sodium sulfite. By means of the controlling agent, respiration and transpiration of leaves can be fully inhibited, accumulation of hazardous substances and dissipation of leaf water can be reduced, and the content of reactive oxygen species can be decreased; oxidation damage to cell interiors can be alleviated, and especially damage to chlorophyllous can be alleviated; through a mutual coordination between sulfhydrylization as well as nitrosation of active proteins and the controlling agent, a higher photosynthetic rate of the tobacco leaves can be maintained, and the intensity of photosynthesis is guaranteed. Experiments and researches indicate that tobacco leaves in the field sprayed with the controlling agent have obviously alleviated states of premature senility, whitening, ambustion and brown spots, and apparently improved physiological and quality indexes; the use effect is obvious, and the controlling agent can effectively prevent the flue-cured tobaccos from being forced to ripen, thereby improving the quality of tobacco leaves.