Abstract: Qinhuangdao 32-6 oilfield is a typical offshore low-amplitude bottom-water heavy oil field. Oil reservoirs with the thickness of less than 10 m account for 22% due to the low amplitude of the oilfield. To produce this kind of reserves efficiently, and based on interlayer logging identification and core analysis, the paper carries out a study on the influences of interlayer on development and well allocation limits of horizontal wells by using numerical simulation method. The study results show that interlayer can effectively block the rapid coning of bottom water when the permeability ratio of interlayer to basement is 0.01; interlayer will allow bottom water to flow around and the producing degree of reserves will reach the maximum when the interlayer area is 2~3 times of oil drainage area in horizontal wells; interlayer will effectively slow down the coning speed of bottom water and meanwhile will enlarge swept volume of water flooding when the interlayer is located in the position with the distance to reservoir top of 3/4 reservoir thickness. Taking cumulative oil production of 5×104 m3 as the lower economic limit for horizontal well allocation, the lower limit of reservoir thickness for horizontal well allocation should be 5 m in offshore low-amplitude heavy oil reservoirs with bottom water. Pilot tests in fields have proved the reliability of the technology, providing technical support for horizontal well allocation in low-amplitude heavy oil reservoirs with bottom water.