The method of making solvent-free bio-based polyurethane topcoat by using solvent-free bio-based polyol resin and modified isocyanate polymer was introduced.The reactivity of isocyanate polymer was reduced by modification.The properties of bio-based polyol resin with different hydroxyl content before and after modification were studied.The most suitable resin and curing agent for the project were screened,and the effects of different ratios of n(—NCO)∶n(—OH)on product properties were studied.A solvent-free polyurethane topcoat with smooth surface,long operation time,excellent flexibility,wear resistance and corrosion resistance was prepared by using FL230 resin with curing agent B and n(—NCO)∶n(—OH)=1.5.