During these years, as the digital TV (DTV) broadcasting technique is developed, the number of set-top box (STB) consumers is increasing quickly, and they spend more money on pay-TV. Conditional Access System is the key technology to realize pay-TV and interact-TV. This paper introduces Man-Machine Interface (MMI) standard of En50221[1] for conditional access system and it’s a method of realization on STB of DTV.