Extended warranty is an optional contract that often provides additional protection for users after the basic warranty expires. Considering the high warranty cost borne by manufacturers and the lack of system availability guarantee, the present study proposes a two-dimensional extended warranty approach for a multi-component series system considering economic dependence. Based on the imperfect preventive maintenance model and the combination of free warranty and pro-rata warranty policies, the manufacturer's and user's warranty cost model and availability model for a single component are established. Considering the economic dependence between multi-components, the preventive maintenance of each component is combined using the grouping maintenance approach. In the case study, we consider the reconnaissance equipment as the research object and use the grid search method to obtain the two-dimensional extended warranty scheme of reconnaissance equipment considering economic dependence. Comparative and sensitivity analyses verify that the approach can effectively reduce the extended warranty cost of the manufacturer and improve the availability of the multi-component system. Additionally, the approach can provide support for warranty cost calculation and system availability estimation under different extended warranty periods.