A well drilling tool able to decrease the pressure at well bottom by hydraulic sucking for increasing the drilling efficiency is composed of drill bit and its short joint segment, low-pressure cavity, jet nozzle, jet cavity and sucking tube. A high-speed jet from said nozzle is generated by the difference between the pressures in drilling column and annular space to form a local low pressure near the nozzle outlet. A sucking tube is used to deliver the low pressure to well bottom.