We study the behaviors of three-dimensional double and triple Weyl fermions in the presence of weak random potential.By performing the Wilsonian renormalization group (RG) analysis,we reveal that the quasiparticle experiences strong renormalization which leads to the modification of the density of states and quasiparticle residue.We further utilize the RG analysis to calculate the classical conductivity and show that the diffusive transport is substantially corrected due to the novel behavior of the quasiparticle and can be directly measured by experiments.