The invention discloses a method for inputting wind field large eddy simulation entrance boundary conditions in complex mountainous area terrains. The method comprises the following steps: determining a large eddy simulation computational domain of a target zone; generating entrance velocity information of the target zone; performing sub-block processing on a computational domain entrance boundary, and then assigning the entrance velocity information to each sub-block through a polynomial interpolation method; monitoring fluctuating wind field characteristics of the practical position of a target zone entrance through a wind velocity monitor, and fitting the characteristics into a wind spectrum through a least square method; performing fluctuating wind velocity composition on the fitted wind spectrum through a harmonic synthesis method, so as to generate a fluctuating wind velocity meeting practical entrance wind field characteristics; assigning wind velocity time interval data taking average and fluctuating wind velocities into account to the large eddy simulation entrance boundary. The method can realize the inputting of average wind and fluctuating wind, properly solves the problem of human-induced cliff during inputting of mountainous area wind field entrance, and gives out the entrance boundary more identical with practical situations.