With the "knowledge economy" era, the theory and practice of calculation and management of enterprise cost is greatly challenged. Great changes have taken place in the structure of product cost, so the traditional cost calculation method cannot reflect the consumption of products, can not provide the correct accounting information for decision and control in enterprises. Activity-based costing is a calculation method of activity-based cost, it resolves the defect of traditional cost method fundamentally, at the same time to the enterprise cost management provides a good foundation, is of great theoretical and practical significance in our research and promotion of activity-based costing. With the "knowledge economy" era, the theory and practice of calculation and management of enterprise cost is greatly challenged. Great changes have taken place in the structure of product cost, so the traditional cost calculation method cannot reflect the consumption of products, can not provide the correct accounting information for decision and control in enterprises. Activity-based costing is a calculation method of activity-based cost, it resolves the defect of traditional cost method fundamentally, at the same time to the enterprise cost management provides a good foundation, is of great theoretical and practical significance in our research and promotion of activity-based costing.