Disclosed a vehicle speed control system using wireless communications, the system including a driving state detecting unit for detecting a driving state and outputting corresponding signals; a transmitter/receiver for outputting low-strength signals; an electronic control unit for receiving the signals of the transmitter/receiver and establishing an ISA mode if necessary, determining if a present driving state corresponds to a first driving state, determining if the driver has performed deceleration operations and performing control into the first driving state if needed; an engine control unit for outputting signals for control of the throttle valve opening; a throttle valve electronic control unit for outputting electrical signals to a throttle valve to control the same; and a display for displaying a present mode and a vehicle state. A method for controlling the system comprises the steps of receiving signals from an RF transmitter/receiver to determine if a vehicle is in a first driving state; establishing an ISA mode and performing display of the ISA mode; determining a present driving state for comparison with the first driving state and performing display to inform the driver of the result of the comparison; determining if the driver has performed a deceleration operation if the present driving state does not correspond to the first driving state; disengaging the ISA mode and enabling full control of the vehicle by the driver if the present driving state corresponds to the first driving state or if the driver has performed a deceleration operation; and controlling an engine control unit via CAN communications if the driver has not performed a deceleration operation.