The invention discloses a protection performance evaluation system and method at a same-tower four-circuit power transmission line. The method comprises: inputting a line structure parameter, access grid information and protection incorrect evaluation factor; controlling turning on or off of all switches of a first group to a fifth group of fault switches to realize controlling of a fault type; for any fault type, setting line lengths and fault point positions between double circuit towers and four-circuit towers; according to voltage levels and locations of all power supplies, adjusting parameters of corresponding transformers and impedors; and carrying out statistics of fault types and line protection actions at occurrence of faults at different positions and carrying out weighted statistics and evaluation on faults and protection actions of all power transmission lines, thereby obtaining a line protection performance quality evaluation report. According to the invention, various fault feature influence factors are considered comprehensively; some operation ways that may cause inaccurate protection actions easily can be avoided; protective setting and key prevention are realized; protection strategies of manufacturers can be protected; and the good support can be provided for secure and stable operation of the power grid.