Taking the purple soil sloping farmland in the seasonal arid area of the lower Jinsha river as the research object, the PR2/6 soil profile moisture analyzer and tipping rain gauge were used to continuously observe the soil moisture content of 0—100 cm soil layers and rainfall during the rainy season, and the purple soil moisture dynamics and its response to rainfall were analyzed. The results showed that there was a significant difference in the monthly average soil moisture content. The soil moisture content of 0—20 cm was as follows: September > August≈July > June, showing an increasing trend throughout the rainy season. The amount of rainfall was the major factor affecting the depth of water supply in soil. Light rain (6.4 mm) only affected soil moisture content above 10 cm, which increased 12.35%; moderate rain (23 mm) affected soil moisture content above 30 cm, and 10, 20, and 30 cm increased by 21.16%, 17.77% and 8.22% respectively; heavy rain (49 mm and 112 mm) affected soil moisture above 60 cm, 49 mm increased by 7.18%~31.12%, 112 mm increased by 34.12%~49.18%. The increased amount of soil moisture in 0—40 cm was significantly correlated with the amount of rainfall and rainfall duration at the level of 0.01; meanwhile, the increased amount of soil moisture in 0—20 cm soil layers was significantly negatively correlated with the drought interval at the level of 0.05; the increased amount of soil moisture in 30—40 cm was significantly correlated with the accumulated rainfall in the previous 3 days. More than 70% of the soil water of purple soil was stored in 60 cm and 100 cm soil layers, accounting for 15.82% and 58.39% of the total soil water storage, respectively. The respond of soil water storage in different soil layers to rainfall was different. The soil water storage of 0—30 cm changed the most in June, the soil water storage of 60—100 cm was relatively stable, while the soil water storage of 60—100 cm changed more than that of 0—30 cm from July to September.