An implementation method and system, main control device and smart card for information transmission are provided. The method includes: the smart card notifying the main control device of the operating mode supported thereby; the smart card receiving a clock frequency returned by the main control device, and if the main control device determines that the smart card can support an externally provided clock frequency, the clock frequency is a second clock frequency; judging whether the smart card itself can support the second clock frequency, and if true, the smart card and the main control device carrying out information transmission based on the clock control signal of the second clock frequency; otherwise the smart card carrying out the transmission based on the dock control signal of the first clock frequency, and the main control device carrying out the transmission based on the clock control signal of the second clock frequency.