Abstract: Modal experiment was carried out on the composite engine block. And the first 5-stage modal parameters were obtained as well as the modal vibration shapes. Results indicate that the natural frequencies of composite engine block are higher than that of metal engine block. Composite engine block has excellent vibration damping property and noise reducing property because composite has strong internal damp and its viscoelasticity can help increase the vibration damp. The transverse vibration of composite engine block was so serious that it was necessary to take measures to improve this defect. It laid the foundation for the structure design and improvement of the composite engine block.