A multi-layer oil reservoir has been developed in a certain operation block of PetroChina in the Americas. After more than 40 years of single layer independent production, each oil reservoir is currently in the stage of ultra-high water cut. Some well areas have been shut down due to the uneconomical exploitation of ultra-high water cut, but there is still some potential for the oil reservoir. In order to further improve the development efficiency of ultra-high water cut reservoirs, this article investigates the main controlling factors and technical boundaries of multi-layer reservoir layer combinations. Through evaluating the production effect and analyzing the production potential of single-layer reservoirs, the feasibility of commingle production in the ultra-high water cut stage of multi-layer reservoirs is evaluated, and target wells for multi-layer commingle production are proposed to guide on-site implementation. Research has shown that the main controlling factors for the division of strata in joint mining development are permeability gradient, effective thickness of strata, interlayer thickness, and single well controlled reserves; The two reservoirs involved in the commingle production of the target well have a span of 206 feet and reservoir pressures of 3036 psi and 3305 psi, respectively. Prior to the commingle production, the daily oil production of the two layers in the target well was 37 barrels per day and 28 barrels per day, respectively, with a comprehensive water cut of 84.7% and 95.5%, respectively; After joint mining, the oil production reached 63 barrels and 54 barrels respectively, accounting for 96.4%, with a daily increase of 52 barrels/day. This article innovatively proposes the commingle production of two ultra-high water cut oil reservoirs. After on-site implementation, the single well oil increase effect is significant, which improves the economy of the single well and also activates the remaining recoverable reserves of the non-economic layer of the target well. It improves the development effect of multi-layer reservoirs during the ultra-high water cut period and provides reference experience for the later commingle production of similar oil reservoirs.