Micro milling force is the main parameter in motoring dynamic cutting process. The natural frequency of dynamometer is the key factor in the accurate measurement of high speed milling force. In this paper, a new structure fixture is designed, and the natural frequency of the fixture is obtained by finite element methods. After optimizing the structure design, the fixture is produced for the force signal acquisition system, together with the forces transducer, signal acquisition card and the software based on the LabVIEW. The experiment shows that the design of the fixture can meet the requirements of force acquisition.