Mechanical study on a fixed tubesheet which are welded with tube bundles and equipment shell using finite element method is performed. Effects of number of tubes on the strength of tubesheet are studied. Variation of the distributions and magnitudes of the stress and deflection of the tubesheet with the size of the unpierced part of the tubesheet are investigated. Results show with support of tubes, the tubesheet does not behave as a flat solid plate in terms of the stress and deflection distribution features. Specifically, If the tubesheet is partly supported with the tubes in the center, the largest stress intensity occurs at the point which depends on the size of the unpierced region. The maximum deflection is near the unpierced region.