Water injection in old oilfields with multiple layers and multiple measures tends to face challenges such as strong heterogeneity and uneven utilization between layers and within layers. How to fully utilize existing production and testing data to accurately identify the layered utilization of reservoirs has become a key issue that needs to be urgently solved for adjustment to oilfield development, comprehensive management, and enhanced oil recovery. In response to the above challenges, the paper, on the basis of seepage theory, proposes a refined production splitting method for small layers of oil wells based on well development history, time-varying production, and measure effectiveness. This method divides the production process into stages based on the well development history of the oilfield. The change in production before and after the measures is used for each stage to calibrate the transformation effect of the treated layers and the total production of untreated layers. At the same time, the splitting coefficient is comprehensively determined by considering the interlayer interference and the non-catastrophic water content in the production process of multi-layer oil wells, and different splitting coefficients are used for production splitting at different stages. Then taking Block W5 in DG Oilfield as an example, this method was applied in the development adjustment. Compared with traditional effective thickness method, KH coefficient method and other splitting methods, the new splitting method has higher accuracy in determining the layered oil and water production, and is more consistent with the results of the liquid production profile. Using this split data to characterize the water drive front of Block W5, and developing adjustment measures to extract the identified remaining oil, good application results have been achieved.