The invention discloses a textile finishing agent with a water-proof effect and a preparation method of the textile finishing agent. The textile finishing agent takes trimethyl phosphite, glyceryl monostearate, polyoxyethylene tri-isostearic glyceride and polyethylene glycol distearate as main ingredients, sulfonated succinic sodium formate, ethyl acrylate, dimethyl phosphate, isophorone diisocyanate, polyoxyethylene, 2,4-dichloro phenoxy ethanol, simethicone, sodium alga acid, titanium dioxide, propylene glycol, a surfactant, a thickening agent and deionized water are added, the processes of heating, stirring, ultrasonic dispersing, ball-milling and reacting under the nitrogen atmosphere are adopted, the waterproofness of a textile is improved and the air permeability is high after the prepared finishing agent is used on the textile, the requirements of the industry are met, and the textile finishing agent has a better application prospect.