We propose a continuously deterministic procurementproduction-inventory model to optimize the raw material procurement and production problem with raw material inventory and finished products inventory when the raw material purchasing price, the production cost, the raw material inventory holding cost, the finished products holding cost, and the demand rate fluctuate over time. We use Hamilton-Lagrange function and Pontryagin's maximum principle in optimal control theory to analyze the model, and we obtain the necessary and sufficiency conditions of the optimal solution to the model. We find some optimal policies regarding the procurement and production under some special circumstances.With the great development of the worldwide market economy, the competitions among manufacturing corporations are becoming sharper. The raw material procurement prices can impose a high influence on tied-up capital and therefore the total cost of final products and company's profit. On the other hand, fluctuations of production costs are commonly faced by many manufacturing firms. If the production policy were not properly managed, the fluctuations could also inflict damages to the firm.Several contributions address the raw material procurement, production, and related inventory policy problems. Khmelnitsky et al [1] state a stationary capacitated inventory and production problem, analyze it in both discrete and continuous time, and give guidelines under which circumstances the models yield similar results, whereas Luhmer [2] formulates a nonstationary control problem considering ordering cost in three settings, backlogging, nonbacklogging, and limited warehouse space. Silver et al [3] and Grubbstrom et al [4] analyze EOQ models to solve the procurement problems. Toktay et al [5] considered a production stage that produces a single item in a make-to-stock manner, in which demand for finished products is stationary. He et al [6] dealt with several inventory replenishment policies for a make-to-order inventory-production problem that consists of a production workshop and a warehouse and Poisson demands. Golabi [7] considered a problem with an independent price process, negligible setup cost, and deterministic but