Rotor–blade parts are the core components of aero-engines, which have the characteristics of complex assembly structure and difficult assembly. Under high temperature and pressure conditions, the rotor-blade assembly error is catalytically amplified, resulting in fatigue cracks and other failures, which seriously affects the stability and reliability of the whole engine. For the rotor-blade structure, traditional variation analysis method cannot comprehensively consider the complex positioning structure and the partial parallel relation, as a result of that a branch chain in the multi-feature parallel structure is often used as a series relationship in a single direction. This paper proposed a variation analysis method of rotor-blade assembly based on the improved Jacobian–Torsor (J–T) model. Firstly, the multi-stage rotational structure, stop positioning structure and tenon tongue-groove structure were analyzed, and the assembly dimension chain considering partial parallel relationship of the rotor-blade with multi-feature was established. Then the assembly joint surface of rotorblade was expressed as the deviation torsor based on the points contact form by using the incomplete positioning strategy, and a united positioning reference scheme based on the positioning point system was established. Finally, the rotor–blade assembly precision index and the solution method based on the improved J–T model was proposed. Taking the assembly precision analysis for radial, axial and circumferential variation of the rotor-blades as an example, the calculation results of the traditional J–T model, Monte Carlo simulation model, and the improved J–T model were compared with the measured data. The results show that the proposed method has higher prediction accuracy than other methods. Compared with the measured results, the error rate is less than 9%. A more reasonable assembling and connecting mode of tenon tongue-groove structure was put forward