Abstract: With the development of performance-based earthquake engineering, the "risk-probabilistic" oriented performance evaluation method has gradually gained the attention of researchers, an important part of which is seismic vulnerability analysis. Vulnerability is often expressed by the fragility curve. By giving the probability that engineering structures exceed a certain limit state under a special earthquake level, it provides a reference for the corresponding performance evaluation and risk decision-making. There are different kinds of vulnerability methods, and more researches focus on how to combine probability theory with earthquake engineering, but the reasonable comparison for the accuracy and applicability of different methods still requires further research. At the same time, the existing vulnerabilities are often based on natural waves, and in-depth analysis is required on the random characteristics and nonstationary properties of ground motions. In addition, existing researches focus on the response evaluation of structures under a single random earthquake, while the structural damage under random mainshock-aftershock sequences still needs to be further explored. Based on the nonstationary random mainshock-aftershock sequences, this paper compares three methods commonly used in seismic vulnerability at this stage: linear fitting method, maximum likelihood estimation, and Monte Carlo method. Then, based on a reinforced concrete frame, a case study is carried out, and the applicability of these three methods as well as the influence of random aftershocks are discussed. Generally speaking, the results obtained by the three methods are similar, and the development trends are relatively consistent, which also proves the effectiveness of these three methods to a certain extent. The Monte Carlo method has a long calculation period, the maximum likelihood estimation is more suitable for the performance level of minor damage, and the linear fitting method is more accurate after excluding the scattered points in the collapse state. After considering non-stationary random aftershocks, the obtained structural vulnerability shows an overall left-shifting trend. If the influence of random aftershocks is not considered, the probabilistic risk caused by earthquake sequences will be greatly underestimated. The corresponding conclusions can provide a reference for the vulnerability selections and aftershock assessments in subsequent studies.