In order to solve the problems that during oil drilling operation, hard and variable geological rocks caused the poor anti-impact ability and was easy to be broken, an adaptive feeding drilling system was presented for coiled tubing which included an anti-stall device (ASD) with safeguard function. ADAMS software was used to simulate the oil drilling process in which the earth layers with various hardness were emulated by alternating force, linearly varying force and constant force and changing law of feeding speed related to different strata hardness was explored.The analysis results show the drilling system can accommodate the strata. The mass blocks with various speeds were employed to hit the drilling bar with or without ASD, which imitated impact of drilling bar on hard strata. The results display that ASD can make the drilling system have good buffering performance and protect the drilling bit efficiently.