The invention discloses a well plunger and belongs to the technical field of oil exploitation. The well plunger comprises a pressure-controlled unlocking plunger body, a steel wire dropping-fishing type insertion sealing working cylinder and a wellhead plunger catcher. The wellhead plunger catcher is located at a wellhead and above the pressure-controlled unlocking plunger body. When the pressure-controlled unlocking plunger body falls into the steel wire dropping-fishing type insertion sealing working cylinder, the pressure-controlled unlocking plunger body is connected with the steel wire dropping-fishing type insertion sealing working cylinder in a hanging manner, and sealing is formed. When the pressure-controlled unlocking plunger body is separated from the wellhead plunger catcher, the wellhead plunger catcher and the steel wire dropping-fishing type insertion sealing working cylinder are separated. When the difference value of the upper pressure and the lower pressure of the pressure-controlled unlocking plunger body is higher than a preset value, the pressure-controlled unlocking plunger body is separated from the steel wire dropping-fishing type insertion sealing working cylinder; and when the pressure-controlled unlocking plunger body is located at the wellhead position, the pressure-controlled unlocking plunger body is connected with the wellhead plunger catcher. According to the well plunger, sealing is formed through hanging connection of the plunger body and the sealing working cylinder so that gas can be accumulated below the plunger body for forming large-enough lifting force. Thus, accumulated liquid discharging efficiency is high.