Abstract: The global economy is transforming from product economy to service economy, and the manufacturing industry urgently needs to shift from low-end production to high-end service in the value chain. At the same time, the new generation of digital information technology is called for to be applied to the upgrading of manufacturing services. For digital servitization, manufacturing firms are faced with the change of internal and external environment brought by digital technology, so it needs to constantly span organization boundaries. because resource liquefaction blurs the internal boundaries of the enterprise, and real-time accessible data repositories enables services to be designed by spanning organization boundaries. Spanning organization boundaries will affect the knowledge conventions and service processes associated with service performance. Whether manufacturing firms can effectively span organization boundary is the key to the success of digital servitization. However, the existing literature has yet to explore when and how manufacturing firms span which boundaries to achieve digital servitization, and has yet to reveal the evolution mechanism about the transformation phases. The paper chooses Sany Heavy Industry as the research object, uses single-case longitudinal study method, and explores the path of digital servitization of manufacturing firms from the perspective of boundary spanning. It finds that the digital servitization of manufacturing firms is a process of constantly spanning boundaries to cope with changes in the internal and external environment of the organization. Following the path logic of "Boundary Identification -- Spanning Strategy - Spanning Ability - Transformation Performance", Sany Heavy Industry mainly goes through three stages: Service 1.0, Service 2.0 and Service 3.0. In the Service 1.0, SANY Heavy Industry identified the Information Boundary and adopted the Information-Sharing Strategy of "Cognitive Update - Process Online - Platform Sharing", which helped form the Service Connection Capability of "Vertical Connection, Horizontal Connection and Internal-External Connection", so as to improve the service efficiency. In the Service 2.0, Sany Heavy Industry identified the Knowledge Boundary, and adopted the Data-Driven Strategy of "Data Aggregation-Data Analysis-Data Utilization", which helped form the Service Integration Capability of "Client-Side Integration, Value-Side Integration and Business-Side Integration", so as to improve the service experience. In the Service 3.0, Sany Heavy Industry identified the Human-Machine Boundary and adopted the Man-Machine Collaboration Strategy of "Machine Learning - Relationship Coordination - Division Of Labor Cooperation", which helped form the Service Collaboration Capability of "Intervention Collaboration, Enhancement Collaboration and Automatic Collaboration", so as to enhance the service value. On the basis of revealing the path model, this paper also finds that the digital servitization of manufacturing firms follows the evolution mechanism named "Demand Perception - Resource Response", that is, the behavior of manufacturing firms to perceive service demand and arrange existing digital resources to respond. In the different stages of the digital servitization of manufacturing firms, there are Perception-Response Mechanism on service development and Perception-Response Mechanism on service delivery respectively. The conclusions of the study provide a new explanation logic and practical enlightenment for digital servitization of manufacturing firms.