Abstract: This study investigated the effects of water retaining agent on the physical and chemical biological character of soil and the root tubers yield of cassava. The cassava cultivar ‘Fuxuan 01’ were used as materials. The water retaining agent was applied on three different levels of 0 kg/hm2, 20 kg/hm2 and 40 kg/hm2 in this experiment. The physical and chemical biological character of soil, the agronomic characters of cassava and the root tubers character of soil, the agronomic characters of cassava and the root tubers yield of cassava were analyzed during the experiment. The results showed that, the water retaining agent could improve physical and chemical biological character of soil, promote cassava growth and increase the yield of cassava. The facilitation of the 40 kg/hm2 water retaining agent was the best which the soil moisture, total porosity, available nitrogen, available phosphorus, available potassium increased respectively by 12.56%, 16.47%, 11.62%, 36.87%, 45.42%; the tree height, stem diameter increased respectively by 14.74%, 12.74%; the yield and economic income of cassava increased respectively by 36.96% and 22.15%. This showed that the water retaining agent play a positive role in improving physical and chemical biological character of soil, promoting cassava growth, increasing the yield and the economic benefit of cassava, it should be applied extends in the planting of cassava.