Abstract: Polyhalite is a kind of resource of potassium.The key problem of extracting potassium from polyhalite is dissolution of potassium in lixiviant. This paper presents the fundamental study of a new method of exploiting-leaching potassium from polyhalite deeply underground in Sichuan Nongle using CaCl₂ solution as solvent.The kinetic process of dissolving potassium from polyhalite was studied by investigating the influence of the leaching conditions such as concentrations of solvent (CaCl2), mineral particle size,and temperature on the process of lixiviation through analysing potassium concentration in the lixiviation solution.The possible lixiviation process of polyhalite was discussed.The recovery of K increased with decreasing mineral particle size and could be higher than 80% under the experimental conditions(mineral particle size:0.42—1mm,initial concentration of CaCl₂:5%, solid to liquid ratio=1/10,tempreture:288—373K).The experimental results showed that the dissolution reaction order was first-order.Apparent activation energy of the reaction calculated was 8.34kJ•mol^-1.The paper establishes that the process controlled the dissolution process is diffusion through the ash layer, and the leaching behaviour can be modelled as a shrinking un-reacted core. This paper introduces the fundamental theoretical and laboratory studies which shows the possibility for extracting potassium from polyhalite underground by leaching.