Abstract: According to reservoir characteristics and development status of TUHA oil field, the auxiliary technology of slim hole sidetracking is studied by optimizing bit and drill stem selection, MWD composite guide drilling, slim hole underreaming, completion string optimization and stimulation technique. By applying the above-mentioned auxiliary technology, the penetration rate of slim hole drilling is significantly improved. The current penetration rate is 95% , higher than that of pase years, and drilling period is cut down by 69%. The time efficiency of complex accidents drops from 14.6% to 1.9%. The set of slim hole drilling auxiliary technology will bring some reference for similar oilfields.