Considering problems existing in the design method of safety factor, in order to maintain the uniformity of design and to keep up with the international standards, a reliability design method is used to design the grounding wire and fittings in transmission lines. Through the reliability calibration of grounding wire and fittings designed by the current national standard GB50545—2010 and the industry standard DL/T5154—2012, the partial coefficients of load and resistance for the grounding wire and fittings under the ultimate state are calculated by selecting the target reliability index. The results show that the average reliability indexes of the lowest sag point and the suspension point are 4.372 and 3.968, respectively, when combined with constant load and wind load, and 3157 and 2.898 respectively, when combined with constant load, wind load and ice load. The average reliability index of fittings is 3.99. The average partial coefficient of grounding wire resistance γRis 1.084, the average partial coefficient of constant load γG is 1.072, and the average partial coefficient of wind load γW is 1.828. The average partial coefficient of fittings resistance γR′ is 1.165, the average partial coefficient of the vertical load of grounding wire γQ3 is 1.062, and the average partial coefficient of the wind load of grounding wire γQ5 is 1.797. If the design method based on reliability theory is adopted, it is suggested that the partial coefficients of grounding wire should be taken as γR =1.1, γG=1.2, and γW=1.8, and the partial coefficients of fittings should be taken as γR′ =1.2, γQ3=12, and γQ5=1.8．