This paper proposes a mathematical model to minimize total inventory cost with considering the additional capital holding cost under the conditions of random demand with normal distribution, quantity discounts for purchasing price and stockouts permitted. On this inventory model, due to multivariate conditions, this paper adopts the multivariate optimization technique and computerize numerical analysis method in solving the research problem. The solution is validated by applying Hessian matrix for the optimality. Finally, several concrete findings and conclusions were drawn for future studies.