The invention discloses an optimized evaluating method for wind power output under a multi-constraint condition for reducing transmission loss. The method comprises the following steps: confirming a factor set influencing the transmission loss of a wind power system, calculating an influence feature of each factor to the transmission loss and forming a hierarchical model containing a scheme layer and a factor layer; dividing the factor set into an invariable factor set and a variable factor set according to a running mode of the wind power system, and confirming a priority matrix by a scheduling operator; obtaining a plurality of feasible schemes by primarily screening according to the change feature of the transmission loss of the wind power system along with the factors; establishing a factor layer membership matrix and a scheme layer membership matrix according to the feasible schemes; and calculating the priority of each of the feasible schemes according to a preset comment set, and selecting the feasible scheme with the highest priority as the optimized scheme. According to the method, the defects of the prior art that a plurality of factors cannot be combined for quantitative evaluation, the transmission loss is high, and the like, are overcome, so that the advantages of combining factors for quantitatively evaluating and reducing the transmission loss are achieved.