Steady-state negative sequence capacity is one of the important factors to evaluate the operation safety and reliability of large turbogenerators. The accurate calculation of steady-state negative sequence loss is the key and the foundation to determine the steady-state negative sequence capacity. This paper introduces the traditional model which simulates the negative sequence operating condition of turbogenerators. And then, a new type of asymmetric load model is proposed to simulate the negative sequence operating condition. The physical mechanism, the advantages and disadvantages of these two models are compared and discussed. Furthermore, based on these two models, the steady-state negative sequence loss of a large 4-pole 1 550 MW nuclear power turbogenerator is calculated by field-circuit coupling nonlinear time stepped 2D finite element method, and the results are analyzed in detail. The results show that, compared with the traditional model, the asymmetric load model presented in this paper takes into account the factors such as the magnetic saturation and the rotor additional loss, which makes the calculated steady-state negative sequence loss closer to the actual situation and establishes the foundation for the accurate assessment of turbogenerator’s steady-state negative sequence capacity.