The crank unit is defined as the basic unit of the crank-group driving mechanism for the modular design and
production, and the balance methods of inertia force are researched on the crank unit in crank-group driving mechanism’s
modular design. The factors affecting the balancing weight’s position and mass are studied. This indicates that the product
of the mass and gyration radius of the balancing weight is influenced by the number, mass, length of the crank and the
total mass moving rod in the mechanism. The balance method based on the crank unit is received to meet the modular
design and production. This approach achieves the balance of crank-group driving mechanism quickly and efficiently.