In order to solve the problem that the cable sag of rigid bracing dome can not be ignored, cables were simulated by catenary cable element.According to Hooke’s law,small strain assuming and deformation compatibility equation,the calculation formula of cable original length was deduced. With any known positive value,the able original length was calculated by dichotomy.For orthogonal cable net,the initial length of cable was compared with known cable original length.The errors are less than 0.16%.And the difference of the calculated cable original lengths is very small for different initial values.According to the form-finding analysis of rigid bracing dome,FEDR method was given to improve the accuracy and reliability of DR method.Solving strategies of form-finding analysis were given.Form-finding analysis program was programmed by FORTRAN language and ANSYS APDL language.Form-finding analysis was done for cable net and the span 71.2 m of rigid bracing dome.Internal forces of rods that were calculated by form finding program were compared with internal forces of rods of finite element analysis software,and the errors are less than 0.42%.
