Abstract: Reasons causing the poor cementing quality and short well life of the sidetracking slim hole were investigated, and the measures taken and reaming techniques were also illustrated.Field practices proved that by conducting the reaming operation after slim hole sidetracking could rapidly remove the contamination zone formed during drilling operation, and minimize the invasion depth of drilling fluid and reservoir contamination, thus improve the production rate.The mud cake on the hole wall formed after reaming was thin and incompact, and could be easily washed out during cementing, thus effectively improve the cementing quality at the second interface and minimize the chances of channeling afterwards.The annular clearance was also enlarged, thus the thickness and strength of the cement sheath was increased, and the oil well life of the sidetracked slim hole was also prolonged.