Abstract: A trolly wire with insulators in electric transmissions isinvestigated in this paper. Based on longitudinal-transversal bendingtheory, the deflection curve equations of aluminum cable steel reinforced isderived. The sag and the horizontal tension of thetrolly wire are obtained based on a insulator's simplified model under deadweight and temperature loads. The results show that the method in this paperis simple and effective. The main influencing factors of the sags aretemperature and span of trolly wire. The average variation rate of the sagto temperature is 2.55mm/^\circC; the sag will be almostincreased by 60% when the span of trolly wire decreases 1%.