The invention discloses a directional diagram numerical optimization method for a round caliber planar-array antenna. The method comprises the following steps that: firstly, according to system parameters, including antenna emission frequency, the caliber shape and size of the array, an array unit interval and the like, establishing the array unit layout of round caliber distribution; according toa wave beam pointing angle appointed by a user, determining the phase weighting of each unit; and then, setting a range weighting optimization vector, initializing the range weighting optimization vector, and adopting a differential evolution algorithm to carry out iterative numerical optimization on the range weighting optimization vector until the fitness value of an optimal optimized vector islower than a set threshold. By use of the method, the numerical optimization problem of the round caliber rectangular grid planar array and a round caliber triangular grid planar array is favorably solved, a required range weighting matrix can be quickly optimized, and directional diagram indexes, including minor levels, null levels and the like, on an array directional diagram, meet indexes.