Abstract: For the ultimate bearing capacity analysis of derrick steel structures, a novel method is proposed based on the partial model updating theory, in which, the test stresses of the main load-bearing member bars are taken as the key indicators and the relevant design parameters as the input updating objects. The dynamic grading load test was performed on the model of laboratory derrick steel structures; the experimental results are compared with the simulative values and an satisfactory agreement is found; the error is within 5%, which verifies the correctness and feasibility of the theory. In addition, the simulation model for some type of derrick steel structures in service is established in association with the grading load test data and the proposed theory; the analog and experimental results show clear evidence of the mechanical behavior being truly reflected. Then the ultimate bearing capacity, failure shape and dangerous position are obtained using the linear buckling, geometric nonlinear and double nonlinear methods.