It is a trend to apply L320 and L360 high-strength angle members in ±800kV ultra high voltage(UHV) transmission lines. The current calculation method does not clarify the failure mode of tension member. Due to the quantities of bolts in the connection, each joint needs to be calculated multiple times, which is inconvenient in engineering. The training sets were established through the tests of multi alignment lines plate members and finite element analysis of large-size angles, and a random forest regression(RFR) model was constructed to perform feature analysis on the section reduction factor. The results show that the weight of adjacent alignment line(Δg1) is too high and for the thickness (t) is low in the current calculation method, which may easily cause significant fluctuations in the results while geometric dimensions of models are changed. The calculation method for section reduction factor is simplified through the optimization of RFR model feature analysis, and the results are stable and more consistent with the FEA models. The predictive model has good generalization ability and could be used in angles with 2 alignment lines in one leg.