The paper deals with modeling methods of frame structures, used in rocket technology. To estimate their inertia, stiffness and strength properties there is a need to create its calculation model. For this purpose now a finite element method is generally used. These models may use various finite elements and combinations thereof. It is obvious that the calculation has found that parameters of the structure under study depend on the selected calculation model. The paper discusses some issues concerning the idealization of elements of the hypothetical frame structure. To simulate the element properties of a longitudinal set (stringers and longerons) and struts as well is offered idealization of beam, because their crosswise dimensions are substantially smaller than the longitudinal ones. Elements of a crosswise force set (frames) represent a welded plate structure that has arch-curved shape of variable cross-section with holes. Welded tubes of different diameter reinforce holes in plates. In vertical plates there are cutouts to mount stringers. To take in full into consideration these features in the rod idealization of frames is impossible. Therefore it seems more appropriate to use plate finite elements to simulate frames. The paper considers two possible frame models the to show their stiffness properties, namely a rod model and a plate one. It shows the advantages and disadvantages of given design schemes of the frame. Based on the test calculations the paper shows which errors in calculating the stiffness properties of the frame under consideration can be obtained using the rod model. Recommendations for judicious use of possible models of the frame at different designing stages are made. To create the studied frame models and their test calculations and analyze the results of calculation was used a SADAS software package developed at the SM8 Department of BMSTU.