Abstract: Gypsum poses significant risks to underground engineering due to its high solubility. The research on the gypsum dissolution in the Cretaceous Guankou Formation(K₂g)is predominantly confined to laboratory experiments, which are unable to represent the true temperature, pressure and hydrodynamic environment. This paper explored the in-situ borehole dissolution test and compared it with the laboratory dissolution test with the flow rate of 1 mL ·min^-1. The results showed that the dissolution rate and the chemical characteristics of groundwater were significantly stratified in the in-situ corrosion test. Specimens at 15 m and 25 m in the borehole exhibited intense karstification, while the dissolution rate at 35 m in the borehole was only 1/4 of the middle and upper specimens. The concentration of SO₄^2- and Ca²⁺ in groundwater at 25 m was more than 1.5 times that at 15 m and 35 m depths, and the ratio of SO₄^2-/Ca²⁺ was lower than that in gypsum molecule. The dissolution rate in laboratory test was half of that in the in-situ test. The p-wave velocity and uniaxial compressive strength of species decreased significantly due to dissolution, and the gypsum experienced a softening process from "elastic-plastic-elastic" to "elastic-plastic". Microstructure underwent a process from integrity to microcrack propagation and disintegration. The differences of dissolution between laboratory and in-situ test were mainly affected by specific surface area, ambient temperature, flow rate and head pressure. The in-situ borehole dissolution test had great significance for the study of the karstification mechanism of gypsum in the Cretaceous Guankou Formation.