Surface mulch is regarded as an effective manner to reducing soil water evaporation, but limited with the adverse influence of plastic film mulch on agro-ecosystems. In this paper, liquid films were prepared with the foundation of kelp as a bio-material. The results showed that the films prepared with the mixture of kelp and polyvinyl alcohol (PA) had superimposed layering structure with tiny pores and gaps, and were stable as well as degradable under field water conditions. The results of the simulative experiments with both of aquic sand-loamy soil and yellow silt-loamy soil that mulching with the film of the mixture of kelp and polyvinyl alcohol (PA) could significantly (P<0.01) reduce water evaporation from soil. It was also found that mulching with the liquid films could increase the water retention capacity of the tested soils. As the initial material – kelp is available, the application of the developed liquid film based on kelp for efficient soil moisture management in agricultural production should be recommended.