The present invention provides a code format of passive radio-frequency identification system, it can be used in a radio-frequency identification system, and contains low-level pulse with one unit length and high-level pulse with n unit lengths, and utilizes regulation of value of n to form different instructions or data formats. The invented code format can be combined with transmission characteristics of PWM and PPM data code and can provide a specific code format so as to make data transmission with specific format protocol. At the same time, it has simple demodulation function, under the condition of limited power supply of passive RFID system can prolong service distance of passive RFID system.