The invention provides a computing method of ice concentration of a transmission line. The method comprises the following steps: the wire temperature and the elastic dependent variable in the fixed span of the transmission line are measured through a fiber grating measuring system; the total dependent variable in the fixed span of the transmission line is obtained according to the wire temperature and the elastic dependent variable; the wire specific load in the fixed span of the transmission line is obtained according to the total dependent variable and the wire specific load is compared with the wire self specific load in the fixed span of the transmission line; if the wire specific load is higher than the wire self specific load, the additional load in the fixed span of the transmission line is calculated; and the ice concentration in the fixed span of the transmission line is obtained according to the additional load. The invention overcomes the problem of higher measuring result error caused by lower measuring accuracy and poorer anti-electromagnetic interference capability due to the adoption of an electric parameter measuring method for measuring stress, temperature and inclination angle in the prior art.