Polymer composites present the behaviours of the viscoelastic under the working temperature of the engines. The space and time have to be taken into account in the calculation because the mechanical components vary with both space and time. In this paper the viscoelastic stresses and the displacements of the composite engine block，which is shaped by moulding of meltable alloy core, were analyzed by threedimension finite element method. The viscoelastic model of the composite engine block was set up and can express the deformation of the block. The accurate stress and displacement fields can be obtained. The calculation results were found in good coincidence with the testing results.