1. A method for generating at least one candidate word string in speech recognition, the candidate word string having a plurality of connected nodes, each node having a node score, a starting time frame and an ending time frame, the candidate word string having a string score obtained by summing the node scores of all nodes therein, the method comprising the steps of: (A) determining an associated maximum string score for each node; (B) sorting all nodes by their associated maximum string scores to group the nodes with the same string score into a same node set; and (C) selecting the node sets with relative high string scores generated in step (B), so as to connect the nodes by their starting time frame and ending time frame, thereby generating the candidate word strings.