The work aims to study the effects of liquid metal modified boron nitride on water vapor transmission and thermal conductivity of aluminum-free lining paper. The functional coating was prepared by the boron nitride filler nanosheets modified by liquid metal and then combined with polyvinyl alcohol. The effect of the liquid metal modification, the content of boron nitride filler and the coating thickness on the water vapor barrier property and thermal conductivity of the inner lining paper were studied. Liquid metal modification solved the problems of boron nitride filler nanosheet agglomeration and matrix/filler interface defects, and further extended the water vapor diffusion path and reduced the water vapor transmission rate. The increase of coating thickness further extended the water vapor diffusion path and reduced the water vapor transmission rate. In addition, the liquid metal modification increased the thermal conductivity and decreased the elastic modulus. In conclusion, the functional coatings improve the barrier and thermal conductivity of traditional non-aluminum lining paper and reduce the modulus, which is expected to provide reference for the preparation of paper with flexibility, barrier and cool feeling.