Abstract: According to the circumstances of an underground nuclear test CHESHIRE at the Nevada Test Site, a model was developed to simulate the dissolution and migration of ²³⁹Pu from melt glass in groundwater. The release rate of ²³⁹Pu was calculated and the released ²³⁹Pu was divided into dissolved fraction and colloid fraction. The pollution plumes for dissolved ²³⁹Pu and colloid ²³⁹Pu were simulated in 100 000 years by software FEFLOW. The results show that the dissolved ²³⁹Pu can’t migration far away from the melt glass and sorption coefficient is the key parameter. If sorption coefficient is more than 10 mL/g, the long distance migration of dissolved ²³⁹Pu can be ignored. The colloid ²³⁹Pu plume will be long-standing in the downstream of the melt glass. The ²³⁹Pu concentration at 1.3 km away from the melt glass would be 10^-2 Bq/L for a long time. The parameters effecting colloid ²³⁹Pu migration are the melt glass release rate, the colloid fraction ratio and aquifer conductivity. It can be concluded that only colloid ²³⁹Pu can migrate far away from the melt glass.