The invention discloses a dynamic spectrum sharing method based on user online learning and low-overhead cooperation, and belongs to the technical field of electromagnetic spectrums. The method comprises the following steps of: enabling a secondary user to acquire frequency spectrum sharing scene information and requirement parameters; then initializing a state parameter and a spectrum sensing parameter of a channel; then, at the beginning of each time slot, enabling the secondary user to judge whether a direct transmission condition is met or not according to the transmission condition of theprevious time slot, selecting to directly continue transmission on the channel of the previous time slot or acquire idle channel transmission according to the channel state and spectrum sensing, andupdate the state parameter and spectrum sensing parameter of the channel; and finally, enabling the secondary user base station to perform conflict coordination according to the channel occupancy condition every a fixed number of time slots. According to the invention, through learning the channel state and the transmission condition by the secondary user, low-overhead and efficient spectrum sharing is realized, the spectrum utilization rate in a high user density and dynamic spectrum environment can be effectively improved, and efficient spectrum sharing is realized.