In the context of uncertain supply of upstream multi component suppliers and uncertain demand of downstream customer in supply chain, researched a problem of how multi-suppliers horizontally supply components synchronously in assemble-to-order (ATO) system. Through investigation and survey in the enterprises and corresponding literatures reviewing, combating theoretical and empirical research methods, using qualitative and quantitative anlysis, systematicly presented a lot of models of synchronously supplying components from the view of multi-suppliers in upstream supply chain.Then proved them through mathematic deduction and Monte Carlo simulation methodology.The synchronous models could reduce inventory waste, improve the fulfillment rate of customer demand orders, increase the incomes of every partners, finally the whole supply chain achieved Pareto improvement.