The influence of dislocation dissociation on the evolution of Frank-Read (F-R) sources is studied using a threedimensional discrete dislocation dynamics simulation (3D-DDD).The classical Orowan nucleation stress and recently proposed Benzerga nucleation time models for F-R sources are improved.This work shows that it is necessary to introduce the dislocation dissociation scheme into 3D-DDD simulation,especially for simulations on micro-plasticity of small sized materials with low stacking fault energy.