The invention discloses a wideband, uvioresistant and highly lightfast finishing agent as well as a preparation method and application thereof. The uvioresistant and highly lightfast finishing agent consists of a benzotriazole and diphenyl ketone ultraviolet absorbent, a defoaming agent, a dispersing agent and water and is prepared by ball milling or sanding, wherein the total content of the ultraviolet absorbent is from 20 to 50 g/L. The finishing agent is used for dyeing a hydrophobic chemical fiber fabric by adopting a dyeing exhaust process, or is finished on the hydrophobic chemical fiber fabric or a hydrophilic fiber fabric by adopting a pad-bake process, thereby increasing the ultravioresistant performance of the fabrics and enhancing the fastness to sunlight of the dyed fabrics. The finishing agent used for dyeing the hydrophobic chemical fiber fabric has high rate of dye-uptake, simple operation, material saving, low cost, less pollution, and obvious effects on increasing the ultravioresistant performance of the fabrics and the fastness to sunlight of the dyed fabrics. The fastness to sunlight of the fabrics dyed or finished by the finishing agent can be increased by 0.5 to 1.