Multimode vortex-induced vibration (VIV) of slender risers, respectively, in stepped and shear flows is explored by finite element simulations. Taking account of the interaction between fluid and structure, a hydrodynamic model is proposed and embedded into the finite element simulation so as to carry out dynamic response of multimode VIV in time-domain. Multimode VIV in both stepped and shear flow fields is examined. In the case of stepped flow, a semi-empirical formula of modal weight is given. In the case of shear flow, modal excitation region can be determined based on modal energy, and participating modes approximately distribute in scattering groups.