In order to promote development of scroll compressor’s high speed and low vibration,and reduce its vibration and running noise,equivalent mechanical model and dynamic balance equation of the principal axis’ s transmission system were set up.Program of parametric finite element model for the principal axis assembly was developed on APDL language,and then its dynamic balance characteristic was improved based on that,and the location（ radius of the centroid R,2, and R,3,） more reasonable of balance weight’s centroid was confirmed. The improving results indicated that,the principal axis could not only keep dynamic balance status,but also adapt more higher working speed,while decreased R,2, and increase R,3,. Because of improving design,the first order natural frequency of the principal axis was increased by 9. 49 Hz,thus then its dynamic characteristic was improved effectively.