Abstract: To improve shield construction efficiency, shield machine key parts should be reasonably selected. Taking the practical case of the successful construction of the first undersea metro tunnel in Xiamen, comprehensive analysis is carried out on the selection of shield machine while passing through soft soil, upper soft and lower hard, boulder, facture zone and other complex strata. Tests and improvement are conducted considering the actual application outcomes. Results show that: shield machine should be equipped with cutterhead telescoping and swing function for seabed complex strata excavation. New center hob design and double independent man gate design should be adopted, scraper protection block should be optimized in square-cone-like shape. The number of stir sticks should be increased, the thickened mud pipe with wear-resistant treatment be adopted. The manual gate valve before the hydraulic ball valve of the slurry pipe should be optimized to hydraulically driven. A mud tank bottom scour mud pump should be specially set up, and the wear resistance of the gravel crusher should be improved. Thus the machine can be adaptive to seabed complex strata excavation.