Abstract: The vendor selection and the order quantity allocation problems with stochastic demand are studied.A multi-objective and stochastic constraint planning model is constructed with the objective functions under three criteria of quality, cost and delivery, and the other goals as constraint conditions with the stochastic demand.By using the weighted way and the penalty function, the stochastic model with uncertainty and multi-objective is converted into a single target optimization model.Then, an improved particles swarm optimization algorithm(PSOA) with inertia and contraction factors is designed to solve the propo sed mo del, and comparative analysis with commonly-used genetic algorithm is given to verify the feasibility and efficiency of the PSOA applied to such issues.

Key words: multi-production purchase, vendor selection, order quantity allocation, stochastic demand, particles swarm optimization algorithm