In this paper, we study the following n-dimensional piecewise smooth differential system
where {\bf x}=(x_1,x_2,\cdots,x_n)^T, 0<\varepsilon\ll1, and g^\pm_i({\bf x}), i=1,2,\cdots,n are real polynomials of {\bf x} with degree m. By using the first order Melnikov vector function, we obtain the upper bound of the number of periodic orbits bifurcating from the unperturbed system.