For shallow reservoirs, the use of extended-reach well technology is often more efficient. However, due to the shallow vertical depth, large horizontal displacement and large change of borehole curvature, the problem of high friction in casing running is prominent, which makes it difficult to successfully run casing to the target depth. In order to meet the requirements of safe casing running in shallow extended-reach wells, the mechanical model of casing running process and the prediction model of extension limit are established based on the classical model of downhole string stress, considering the influence of friction resistance, borehole bending and casing buckling. The mechanical resistance and extension ability of casing in shallow extended-reach well are analyzed. This paper evaluates the running ability of casing of different sizes in extended-reach wells in Bohai oilfield, and puts forward the safe running countermeasures. The research results can provide theoretical reference for casing running in shallow extended-reach wells.