Completely weathered argillaceous limestone has complex composition and special structure. When countered water， it is easy to be soften and distingrate， and its strength is rapidly reduced， which is very easy to induce various engineering geological disasters. Taking the completely weathered argillaceous limestone in Dajiangou area of Jinan as the research object， the engineering geological characteristics of the completely weathered argillaceous limestone are studied from the physical， mechanical and hydraulic aspects through the combination of field investigation and laboratory test， moreover， the stability of the hole wall during the drilling process is evaluated based on the discrete element software PFC. The correlation between the stress in the hole and the grouting pressure is obtained， which provides reasonable suggestions and references for the future pile foundation construction. The results show that the completely weathered argillaceous limestone has poor water resistance and is easy to disintegrate， and the water content has a significant impact on the disintegration rate. With the increase of water content， the shear strength of completely weathered argillaceous limestone decreases exponentially， and the deterioration of strength is obvious. Under dynamic disturbance， the internal unit of completely weathered argillaceous limestone is seriously damaged. It is recommended to set the mud pressure at 0.3MP， which can generate relatively obvious normal contact force on the hole wall without causing soil damage， and provide better support for the stability of the hole wall.