Abstract: Water cycle and balance of carrying soil is an important issue in the research of biotechnical slope protection. This paper takes the carrying soil with matrix as the research object to carry out evaporation test. The moisture content is measured at different depths of the slope. Moisture content changing with time under the natural sunlight is observed. This paper uses the micro-lysimeter to test the evaporation capacity at different thickness, slope, temperature and ratio of matrix of carrying soil. The result is used to analyze influence factors of evaporation capacity. The results show that the time of carrying soil with water holding agent and peat being saturated is significantly shorter compared with no water holding agent and peat, which indicates that they increase the water imbibition of carrying soil. However, the addition of water holding agent and peat soil also reduces the weight of soil. Eleven days cumulative evaporation of samples with 0.2%water holding agent is 21.2mm higher than that of samples with 0%water holding agent. It indicates that 0.2%water holding agent and 12%peat can effectively reduce the rate of evaporation and water desorption. Moisture content presents periodic change over time. In addition, the moisture content is different at the different depths of samples. Among the influence factors, the temperature is the direct influence factor to the evaporation of carrying soil. The gradient and thickness affect evaporation through influencing the water content. At the same time, they also control the energy supply of evaporation process. But the big slope gradient and thickness are not conducive to the slope stability of carrying soil. It is recommended that the slope gradient of carrying-soil spray seeding be less than 1︰0.75 and the thickness be controlled between 10cm and 20cm. So it can greatly increase the available water holding capacity of vegetation. The above research can provide the basis for the biotechnical slope protection.