As the key technology of reliability evaluation for hull structure in-service, the merits of the reliability assessment theories determines the effectiveness and confidence level of the reliability evaluation result directly. The development course and current research situation of traditional reliability assessment theories and non-probabilistic reliability assessment theory were elaborated in the view of calculation principle, computing of measurement index and engineering application. Simultaneously, the advantages and disadvantages of all current reliability assessment theories that applied in hull structure in-service were analyzed and summarized. The future research outlook was developed and the focus in the study of hull structure reliability was outlined.