Quantitative analysis of frequency tripling based on the transform of phase aberrations is presented to study the influence of medium-high phase errors on focal spot tails. Nine-fold increase of energy fraction of high-order spectrum caused by the noises in the "waviness-1" regime would result in power growth of 3'omega' tails and significantly enlarge the spot size from 1'omega' to 3'omega' laser. The power growth in "waviness-1-2" regime (0.1-0.4 mm^(-1)) is with main responsibility for the increment of 3'omega' spot tails, as noises in whole "waviness-1" portion answer for the growth of 1'omega' spot tails. Theoretical predictions are shown to be consistent with numerical simulations on focal spot with variant phase ripples and different B-integral values.