An OmniChannel (OC) consists of two or more channels hence, a single item can exist in multiple channels simultaneously which increases the difficulty of demand forecasting and inventory management in the OC. Therefore, how to specify an appropriate inventory strategy for an omnichannel with multi-channel demand has become one of the most critical issues facing omnichannel retailers. The inventory can be controlled in the OC by applying an efficient Distribution Requirements Planning (DRP) policy. Here, we extend this policy to an omnichannel and adjust it to have the right items, with the right quantities, and at the right location to meet predicted demand to minimize back-orders and reduce the transportation and holding costs. To obtain this goal in an OC retailer; by fixing the replenishment time, the optimal replenishment level of items is determined by considering their demand in all channels simultaneously.