A method, a controller, and a system for service flow control in an object-based storage system are disclosed. The method is: receiving, by a controller, a first object IO request; acquiring a processing quantity threshold and a to-be-processed quantity; if the to-be-processed quantity is less than the processing quantity threshold, sending the first object IO request to a storage device client, and updating the to-be-processed quantity; receiving a first response message replied by the storage device client for the first object IO request, where the first response message carries a processing result of the first object IO request; and adjusting the processing quantity threshold according to a received processing result of an object IO request when a preset condition is met. The storage device is not overloaded with object IO requests and can use all resources to effectively, thereby improving performance and a success rate of the object-based storage system.