1. A method for processing a data stream in a stream computing system, wherein the stream computing system comprises a control node and multiple working nodes, the method comprising: invoking, by the control node according to a configured parallelism degree for each working node, one or more working nodes of the multiple working nodes to process the data stream; collecting, by the control node, data traffic information between each working node of the one or more working nodes and other working nodes, and processing speed information for each working node of the one or more working nodes; determining, by the control node, an optimized parallelism degree for each working node of the one or more working nodes according to the collected data traffic information and processing speed information; and determining, by the control node, whether the optimized parallelism degree for each respective working node of the one or more working nodes is the same as a parallelism degree of the respective working node, and if the optimized parallelism degree of the respective working node is not the same as the parallelism degree of the respective working node, adjusting the parallelism degree of the respective working node according to the optimized parallelism degree of the respective working node.