Optical manipulation is a useful method for controlling micro-objects in parallel and remotely. We apply optical manipulation to control of the position and reaction of DNA by making microdroplets that contain DNA. The microdroplets can be transported and fused by contacting each other. Use of microdroplets is an effective way of controlling DNA reaction, because it enables to compartment reaction volumes and to execute reactions at local space. We use the microdroplet-based reaction method to implement photonic DNA computing.