The invention discloses a prepositive stamping method and system of a high-precision timestamp. The method comprises the following steps: S1, detecting a data packet frame header during data transmission; and S2, once a frame header termination mark is detected and data packet contents are not starting to be received, taking a real-time clock value of the moment as the timestamp. By means of stamping before the data packet contents are received, the time fluctuation due to different data packet lengths in the traditional postpositive stamping manner is avoided, meanwhile by adoption of the method disclosed by the invention, the stamping time standard is also unified to reduce the difference caused by the different data packet lengths, in addition, a high-precision crystal oscillator is used as a counter, and the timestamp is indirectly obtained by indirectly calculated by time correction, so that the accuracy and the stability of the timestamp are greatly improved, and the accuracy requirements of the modern information technology for the data can be met more conveniently.