A method is proposed for managing defect areas on an erasable optical disc in a dynamic manner. By this method, a main spare area including a plurality of logical blocks is used to provide substitution logic blocks for any bad logical blocks in the user read/write area; and when all the logical blocks in the main spare area are used up, a supplementary spare area is defined from a continuous unused storage area in the user read/write area; and further, when all the logical blocks in this supplementary spare area are used up, an additional supplementary spare area is defined from another continuous unused storage area in the user read/write area; and so forth. The method allows the use of a comprehensive set of commands and data message for the communication between the file system and the optical drive when performing this management method. This method allows the optical drive to move over a shorter distance from a bad logical block to the substitution logic block so that access time to the optical disc can be enhanced. Moreover, this method allows all the bad logical blocks to have substitutions as long as the unused storage space in the formatted area is sufficient, so that this method can offer a much longer time of service than the prior art.