In light of the difficulties in secondary cementing of ?88.9mm small casing set in ?139.7mm production casing in the Changqing Oilfield， such as small annulus， high pumping pressure， thin cement ring， uncertainty in sealing integrity for the follow-up treatment measures， poor wellbore boundary， poor cement bonding at the two boundaries， technological innovation and improvement was conducted to develop a low-friction， pressure-resistant and leak-proof cement slurry system， and a thermosetting resin cement slurry system. They were combined with the independently developed boundary enhancing acid flushing fluid and the cementing plugging fluid system to form the slim casing cementing fluid system in Changqing Oilfield. With optimization of the reliable cementing accessories and the structure of the small casing cementing string， and use of the single-stage cementing process according to the principle of balanced pressure cementing， the slim casing secondary cementing process has been developed. Field application in 10 wells showed the rate of excellent cementing quality up to 95% with significant stimulation effect， which can provide strong technical support for the potential enhancement of the old wells and the management of casing damaged wells in Changqing Oilfield.