The invention relates to the field of petroleum and natural gas tight reservoir rock core analysis, and the method considers that salt crystallization occurs in a rock sample in the process of takinga water-soluble salt reservoir rock core from a stratum temperature and pressure condition to a ground temperature and pressure condition, so that salt leaching treatment needs to be carried out on the rock core before parameters such as porosity are tested. According to the method, only the salt content influencing the porosity due to the crystallization effect in the process of taking an in-siturock sample to the ground can be cleaned so that the porosity of the rock core tested after salt leaching is objective and real, the formation water mineralization degree is determined through adoption of the mass conservation principle, so that a foundation is laid for follow-up tight reservoir experiment evaluation, and the method is an experiment method in the aspect of rock core analysis in the petroleum and natural gas exploration and development process.