We analyze the nonlinear optical properties in Weyl semimetals which result from the intraband and the interband contributions around the Weyl points respectively. Based on the Boltzmann equation and the Floquet method to the Schrödinger equation under the tight-binding model we can calculate any order of nonlinear optical conductivity in the Terahertz regime with the effective chiral Hamiltonian used. We find that the influences of the interband transition and intraband term on the optical properties of the system are opposite each other when increasing frequency and interband transitions dominates the optical responses. The part of the linear conductivity of the system which is contributed from the intraband electric motion increases when the relaxation time reduces and the part of the linear conductivity from the interband transitions increases with the decrease of the temperature. The part of the third harmonic generation which is contributed to the interband transitions is proportional to ω−3 and will be considerable when the frequency become small enough. The nonlinear terms enhance the optical reponses of Weyl semimetals and provide more information about the critical properties.