In pursuit of the optimal maintenance cost-availability ratio for large engineering equipment during a two-dimensional extended warranty (TEW) period, this paper puts forward a joint preventive maintenance (J-PM) strategy executed by both users and manufacturers. By deriving the dynamic evolution of the product's two-dimensional failure rate function, a maintenance cost-availability ratio model is established. Subsequently, pattern-seeking methods and genetic algorithms are utilized to solve the cost-availability ratio model, yielding the optimal combination of decision variables. A comparison is made between the proposed J-PM strategy and preventive maintenance (PM) strategy executed solely by users or manufacturers. The results prove that the J-PM strategy can reduce the maintenance cost-availability ratio more effectively and achieve better maintenance outcomes, thereby validating the superiority of the J-PM strategy.