In order to evaluate the influence of component parameter uncertainty on the reliability of HVDC transmission system, this paper presents a reliability interval evaluation method for HVDC transmission system based on affine arithmetic (AA). Firstly, the interval form is used to describe the uncertainty of component reliability parameters, an interval algorithm expression and a reliability interval evaluation model of the HVDC system reliability indices are established. Then, considering that the result of interval arithmetic is too conservative, AA is introduced into the reliability evaluation of HVDC transmission system. Finally, through the analysis of double 12 pulse HVDC transmission system, it is proved that the proposed method can effectively describe the influence of component parameter uncertainty on the reliability evaluation of HVDC transmission system, which can provide a better reference for practical engineering, the weak components of the system can be identified efficiently.