Double-tubesheets are used in heat exchangers where strict tightness is required. In this paper, finite element analysis models were established to simulate the double-tubesheets. Stresses and deformations in the tubesheets induced by pressure load were calculated and formulated. Results showed that the tube supports to the tubesheet are much stronger than considered in the commonly used heat exchanger design codes. If the design is based on accurate stress analysis using finite element method, the tubesheet thickness of heat exchangers could be significantly reduced. The two tubesheets strengthen each other especially when their spacing is short.