The invention discloses a line mountain fire disaster assessment method without the real-time acquisition of field information. The method comprises the steps of determining a vegetation type and a vegetation height, judging fire scene fire behavior type, obtaining alarm transmission line information, obtaining meteorological data of a mountain fire position, calculating mountain fire flame zone, ion zone and smoke zone heights, calculating flame zone breakdown voltage, calculating ion zone breakdown voltage, calculating smoke zone breakdown voltage, calculating transmission line trip probability, and evaluating a mountain fire level. The invention also provides a line mountain fire disaster assessment system without the real-time acquisition of field information. The method and the system have the advantages that a bearing body transmission line parameter, a mountain fire internal fire behavior characteristic and external environment conditions are considered, an accurate line fault probability model is established, use data is obtained based on a forestry database and a meteorological data value calculation result, the field acquisition is not needed, the probability quantitative calculation of transmission line trip caused by mountain fire is realized, the adaptability is high, and the mountain fire disaster resistance ability of a grid is improved.