Dissolution experiment of salt rock and mud-containing salt rock from some extra-deep stratum was made under normal temperature and high temperature using self-made devices.And it was found out that the density of solution was exponentially decaying with time,some parameters were obtained by fitting.The dissolution rate of salt rock is 1.26 times of that of mud-containing salt rock under normal temperature,and the dissolution rate of salt rock under 86℃ is 2.32 times of that under normal temperature,while the dissolution rate under 50℃ is 1.49 times of that under normal temperature.Based on the mass conservation principle,the function relationships between dissolution rate and the density of solution under normal temperature and high temperature have been deduced.The experimental data present that the relationships between dissolution rate and the density of solution under normal and high temperature can be considered to be linear approximately,and the parameters have been fitted which are useful to the model of the process of dissolving cavity.