This paper considers a supply chain model comprised of two suppliers and one manufacturer in Assembly-To-Order environment. Under the uncertainty of component supply and customer demand, it investigates how to come into component horizontal synchronization between multi-suppliers from the perspectives of suppliers, and supply components in set to manufacturer, which could decrease the manufacturer's expected total inventory cost. Firstly, it presents the theory model in single-period and multi-period, and compares the expected total inventory cost before and after synchronization. Secondly, through the simulation method, it validates and compares the models, and analyzes the different shortage cost's impact on optimal order quantity, optimal order-up-to level and minimal expected total inventory cost. Finally, the result shows that component horizontal synchronization between multi-suppliers could decrease the manufacturer's expected total inventory cost and improve the response to customer's demand.