Work method is an enterprise's operating activities or assets of real use depreciation as the basis. In principle, work method is in line with the economic substance of depreciation method, especially suitable for contact with the output value of fixed assets transfer, thus the output distribution of depreciation expense is reasonable. This kind of method for service efficiency fluctuates according to degree of use of assets depreciation is ideal, but some limitations exist in use, because the assets can provide services are sometimes difficult to accurately evaluate the number of expected.