In order to provide theoretical basis for improving selenium content in soil and plant, the effects of different concentrations of phosphorus on selenium uptake and accumulation of pakchoi in two main selenium-rich soils of Guangxi and the morphological transformation of soil selenium were studied by soil culture pot experiment in which four phosphorus concentration gradients were designed for Se-rich latosolic red soils (Guiping City, Guigang City) and red soils (Yongfu County, Guilin City) in Guangxi. The results showed that the same phosphorus treatment had different effects on selenium uptake of pakchoi in different soils. Low phosphorus treatment (P50, 50 mg/kg) was beneficial to selenium uptake of pakchoi in Se-rich latosolic red soils. Selenium content in the aboveground part of pakchoi was the highest in P110 treatment (110 mg/kg), while that in the underground part was significantly lower than the control group in Se-rich red soils. At the same time, selenium transport by applying phosphorus to pakchoi was also different in the two soils. In Se-rich latosolic red soils, when the amount of phosphorus was less than 80 mg/kg, the application of phosphorus inhibited selenium transport from underground to aboveground, but selenium transport was promoted in Se-rich red soils, and both peaked at P110. The difference of selenium content in plants depends on the effective form of selenium content in soil. The results showed that the application of phosphorus significantly increased the contents of water soluble and exchangeable selenium in soil, and selenium content in pakchoi was consistent with the water-soluble selenium in the soil, different phosphorus treatments had different rules in selenium morphological transformation in the two soils, which provides a reference for further study on the interaction between phosphorus and selenium.