The notion of difference for two convex compact sets in Rⁿ, proposed by Rubinov et al, is generalized to R_m×n. A formula of the difference for the two sets, which are convex hulls of a finite number of points, is developed. In the light of this difference, the relation between Clarke generalized Jacobian and quasidifferential, in the sense of Demyanov and Rubinov, for a nonsnooth function, is established. Based on the relation, the method of estimating Clarke generalized Jacobian via quasidifferential for a certain class of function, is presented. AMS Mathematics Subject Classification : 52A20, 65H, 90C30