This thesis applies the PSO method to solve the company's problem of ineffective control of material cost at Betrimex through data and interviews to find the first symptoms. Next is to locate the potential problems and through the survey to evaluate the influence of each possible problem and conclude to find the main problem. From the main problem continue to apply fishbone diagram to find the causes and locate the main cause. From there, give appropriate solutions as well as corresponding action plans. For each analysis, the main decision is based on data, company reports, group interviews, individual interviews as well as surveys to choose.