With biochar modified by adding different types of water retaining agent polyacrylamide(PAM,a material with strong ability of water retention and cohesiveness) such as MW polyacrylamide,cationic poly-acrylamide and anionic polyacrylamide,this article analyzed the influence of the biochar modification on the soil's water evaporation and maize growth in seedling stage.The results showed that the evaporation of soil water decreased by 4. 1%with 3%biochar application after two weeks while the soil water content significandy increased by 39.7%and 50.4%with 2.5%and 5%biochar application in potting soil respectively.And with modified biochar application in the potting soil,the water-holding capacity significantly increased with the potting soil water content 10.5%to 63.0%higher.The order of the water absorbency with three modified biochar 2:10>1.5:10>1:10 showed that the water absorbency increased with the ratio of PAM addition.The highest water absorbency was found with the MW polyacrylamide while that with 2.5%and 5%modified biochar application significantly increased by 54.3%-84.0%and 119.5%-145.1%respectively. Taking consideration with soil water retaining and plant growth 2.5%modified biochar application was chosen to use in the agricultural production.