In this paper, we will study an important property on the regularity of the trajectories of the stochastic flow generated by a famous model in finance. More precisely, we prove the differentiability with respect to initial data of the solution of the stochastic differential equation associated with this model based on Gronwall's lemma, Ito's isometry and Burkholder-Davis-Gundy's and Holder's inequalities. This is the main motivation of our research.