In order to further research the application of γ-PGA in agriculture, different contents of γ-PGA (0, 0.1%, 0.2%, 0.5% and 1%) were applied in sandy loam and silty loam without granular structure to study the effects of γ-PGA on soil physical structure and water retention characteristics. Results showed that: with the increasing of γ-PGA content, water retention capacity of soil increased under the same absorption force. Values of α in the VG model were all larger than those in the control group, and n value decreased progressively. When the content of γ-PGA increased to 1%, the bulk density of sandy loam decreased by 0.087 g/cm3, and the porosity increased by 3.28%; corresponding parameters of silty loam were 0.108 g/cm3 and 4.08%, respectively. The addition of γ-PGA reduced the proportion of capillary pore, and increased the proportion of invalid pore, indicating that effect of γ-PGA on the physical characteristic of silty loam were greater than those of sandy loam. Power function positive correlation existed between the saturation moisture content and the γ-PGA content, while negative correlation existed between the saturation diffusion rate and the γ-PGA content. The relative error between the saturation diffusion rates calculated by parameters of VG model and horizontal infiltration method was smaller than 10% in silty loam. Except for the wilting coefficient, γ-PGA had significant effects on other soil water constants, wherein the constants increased with the increasing of γ-PGA content. In the soil, proportions of film water and capillary water increased, whereas the proportion of gravitational water decreased significantly. When the γ-PGA content was 1%, the proportion of available water was 64.83% in silty loam, whereas the value was only 56.14% in sandy loam. Adding γ-PGA was beneficial to improve pore distribution in soil and water retention capacity, and prevent deep seepage of soil moisture.