Abstract: Fracturing in slim hole and casing deformation wells is different from the fracturing in general holes. It needs to be equipped with the downhole tools of minor diameters and wellhead devices resistant to high pressure, reauires a lot on the carrying capacity, anti-shear performance, and the performance of reducing friction. In order to solve the difficulties in fracturing in slim hole and casing deformation wells,according to the specialty of slim hole and casing deformation wells and the reality of minor diameter downhole tools,the Y341-70 packer and K341-98 packer are developed and the design of downhole technique string is accomplished for ?89 mm and ?127 mm casing slim hole wells and ?139.7 mm casing deformation wells. The fracturing fluid and fracturing operation are optimized. The technology is successfully accomplished on more than 40 wells and achieves good effect.