An electric field induced dynamic phase-matching which can improve the thickness tolerance of waveguide SHG device is first demonstrated using organic nonlinear optical (NLO) materials with low glass transition temperature (Tg). The advantage of this technique is the possibility to control an effective refractive index of NLO waveguide at room temperature. As a result of refractive index variation induced by an external electric field, the effective phase-matching dimension can be controlled from 1.272 mu m to 1.260 mu m. The phase-matching condition i.e. conversion efficiency of second harmonic light can be easily tuned by changing a poling electric field. The obtained net conversion efficiency of low Tg NLO slab waveguide was found to be 1.5 %. No decay of conversion efficiency for low Tg NLO waveguide is observed in the presence of an electric field.