The invention provides a data communication method and system. A first terminal starts to detect a first phase difference value of a waveform phase of a communication carrier signal relative to a first start phase when sending a to-be-processed data packet completely, and receives an answer data packet only when the first phase difference value meets a threshold range; a second terminal starts todetect a second phase difference value of the waveform phase of the communication carrier signal relative to a second start phase when receiving completely, and sends an answer data packet only when the second phase difference value reaches to a delta phi; the first terminal and the second terminal simultaneously receive and send data via detecting a phase difference, so the accuracy of timing ofboth parties is greatly improved; and thus, the first terminal and the second terminal are guaranteed to receive and send the answer data packet only at a special high-precision moment, the risk thatthe data received by the first terminal are falsified by the outside in a transmission process is avoided, and the reliability of the answer data packet received by the first terminal is improved.