Using the threedimensional software ANSYS WorkBench for nonbeam pumping unit for dynamic analysis, the threedimensional finite element model of the pumping unit rack was established. To ensure that the system could be fully reflected in the dynamic analysis of the characteristics of its own force , firstly , the software prestress modal frame was used to analysis the pumping units static characteristic, and then the module was used on the rack's modal analysis, the rack's front nine natural frequencies and mode shapes were obtained. The results showed the Prestress had a little influence to the intrinsic characteristics of rack, and it could be neglected, and the rack structure affected the overall stability of the rack|through the analysis, changing the form and structure of the rack scantlings could improve the system's stability. Thereby the life of the rack was enhanced.