Abstract: Fine layered fracturing is required to tap the potential of the remaining oil controlled by wells with casing damage occurred during oilfield development. However, as the wellbore diameter of casing damaged wells is locally reduced, it is impossible to implement the conventional fine layered fracturing process. In this paper, an Ø95 mm small-diameter packer is developed, and in the development of which, the rubber reinforcing agent of the rubber cylinder is carefully selected, the cord combination is optimized, and the steel body is treated with salt bath quenching heat treatment process, as a result, the overall pressure-bearing capacity and fatigue resistance of the packer is effectively improved. In addition, a small-diameter pressure transmitting sandblaster is developed, and the sandblasting port is designed with an inclined cross-sectional and multi-hole structure, which effectively reduces abrasion. A tubing blowout prevention valve is designed, and a repeated switch and sealing mechanism are also innovatively designed in this paper. It has been proved in laboratory and field tests that the fine layered fracturing process string used in the casing damaged wells has achieved the overall temperature resistance of 120 ℃, a pressure-bearing capacity of 70 MPa, the sand adding capacity of a single sandblaster of 230 m³. Besides, the fine layered fracturing of 11 intervals can be realized by running the string in a single trip, which can meet the fracturing requirements of casing damaged wells with a restricted diameter of more than 100 mm. This technology has been applied in 109 wells in Daqing Oilfield, with a success rate of 99.1%, and the average daily oil production increase of a single well after fracturing is more than 5 t/d. This fracturing technology plays an important role in the fine tapping of the remaining oil in the casing damaged block and the improvement of the injection-production well pattern in the late stage of the development of the mature oilfield. At the same time, this technology can also be prompted to the fine layered fracturing of small cased wells with the same wellbore diameter.