It is difficult to evaluate the infill well productivity of multi-layer reservoirs in old offshore oilfields due to the interlayer heterogeneity of producers and water breakthrough at the initial stage of production. Interlayer interference coefficient is usually used to describe the effect of commingled production on infill well productivity in multi-layer reservoirs.However，the interlayer interference coefficient can hardly be quantitatively characterized. To solve this，with dynamic and static data from old offshore oilfields，we propose a new method to evaluate the infill well productivity of multi-layer reservoirs. The paper introduces the concept of injection-production affection efficiency. A method that analyzes the injectionproduction affection efficiency of multi-layer reservoirs is worked out by integrating modular dynamics test（MDT）results，production logging test（PLT）results，logging interpretation results of water-out reservoirs，and static geological knowledge. By the method，the unaffected layers without contribution to stable productivity can be identified. Furthermore，the dynamic relative permeability is used to calculate the dimensionless liquid productivity index，macroscopically characterizing the effect of interlayer heterogeneity on infill well productivity of commingled production at different water cuts. The chart and process of evaluating infill well productivity of multi-layer reservoirs in old offshore oilfields at different water cuts are established. The reliability of this method is verified by productivity analysis of newly infill wells in Block N of Bohai A Oilfield. The flow coefficient lower-limits of infill wells at various production goals are charted to guide the primary selectionof infill well location.