Abstract: The heavy load angularly defecting milling head is an important functional component of 5-axis CNC machine tool,which is used for large and complex parts with free-form surface processing.The paper constructs the architecture of key technology for heavy load angularly defecting milling head based on demand of independently developing of milling head.The architecture includes theory investigation and experiment analysis.Theory investigation is the base of the architecture,which includes kinematics analysis,static analysis,dynamics analysis,thermal characteristic analysis and thermo-mechanical coupling analysis.Experiment analysis verifies the theory investigation,which mainly includes modal testing,thermal characteristic experiment and precision experiment.The paper focuses on elucidating the architecture of all key technology of milling head,the following papers will discuss the detail of the key technology respectively in the architecture.The study will provide academic and technical support for milling head design.