The invention relates to the technical field of cotton seed coating agents, and a seedling-protecting and growth-promoting cotton seed coating agent and a preparation method thereof and the application thereof to control of pests and diseases and cold resistance. The seedling-protecting and growth-promoting cotton seed coating agent comprises the following raw materials: acephate, carboxin, thiram, a wetting and dispersing agent, a microfertilizer, a plant growth regulator, an antifreezing agent, a defoaming agent, a thickening agent, a film-forming agent, a dyeing agent and a preservative. The seedling-protecting and growth-promoting cotton seed coating agent can effectively promote the growth of cotton seedling roots, increase the emergence rate and the seedling survival rate of cotton and improve growth and low temperature resistance of seedlings, has a relatively good control effect on the pests and the diseases in the cotton seedling period, and can increase the cotton yield. Through the use of the seedling-protecting and growth-promoting cotton seed coating agent, the using amount of a pesticide and a fertilizer can be reduced, and the seedling-protecting and growth-promotingcotton seed coating agent has the advantages of safety, convenience and pollution.