A method and system for improving a channel change rate using a conditional access table/program map table (CAT/PMT) to be transmitted in an out-of-band (OOB) band. First main data including a channel ID of a scrambled channel and Conditional access table (CAT) information corresponding thereto and defining a version is transmitted from a main program of a conditional access system (CAS) headend. Second main data including the channel ID and Program map table (PMT) information corresponding thereto and defining a version is transmitted from a main program of a demux/remux device. Third main data generated by receiving and combining the first and second main data is included in service information (SI) and is transmitted in an Out-of-band (OOB) band. After extracting only the third main data from the transmitted Service information (SI) in response to a channel change event signal, encrypted broadcast content of each channel is released and provided to a user.