A method for improving variable length decoding performance is provided. A variable length decoding module decodes a coded data to obtain a decoded data and a subsequent module receives the decoded data to perform further processing. A buffering module is coupled between the variable length decoding module and the subsequent module, and buffers the decoded data decoded by the variable length decoding module. A read part of the buffering module is cleared so that a content of an unused area of the buffering module is a predetermined value when the subsequent module reads the decoded data from the buffering module, wherein the unused area is a part of the buffering module except for the unread decoded data. The variable length decoding module does not write zero values of the decoded data into the buffering module when the variable length decoding module reads a zero output instruction among the coded data.