Abstract: The optimization of casing program is one of the important measures for the cost reduction and efficiency increase of well drilling and completion. The advantages and disadvantages of two casing programs which are currently used in the conventional directional wells of Bohai Oilfield were demonstrated, i.e., Ø444.50 mm hole (Ø339.73 mm surface casing)+Ø311.15 mm hole (Ø244.47 mm production casing), and Ø444.50 mm hole (Ø339.73 mm surface casing)+Ø250.82 mm hole (Ø177.80 mm production casing). Then, the casing program of Ø311.15 mm hole (Ø273.05 mm surface casing)+Ø241.30 mm hole (Ø193.67 mm production casing) was put forward and its feasibility of drilling and completion was demonstrated. Field application indicates that compared with the neighboring wells, the rate of penetration (ROP) of the well with optimized casing program is increased by 35.8% and the single-well drilling cost is reduced by RMB 2×10⁶ yuan, presenting remarkable achievement of cost reduction and efficiency increase. Therefore, its application prospect is promising.