Meteorological factors will cause the transmission line fault and affect the power system reliability prominently. The original reliability parameter model which considered the meteorological factors is improved, and it is pointed out that transmission lines in different geography have different average failure rate, and their corresponding three kinds of weather and the percentage of number of failures under the three kinds of weather also show great difference. Connection number is used to deal with the uncertainty of reliability original data and weather conditions. RBTS is evaluated with state enumeration method, and the reliability indices in form of connection number are obtained. The result shows that the uneven geography and meteorology will affect the reliability evaluation of the transmission system greatly, and the reliability indices in form of connection number also give the uncertain part, which proves the reliability of the proposed method.