Abstract: In order to solve the rod jammed problem in the borehole driling operation of the drilling and loading machine, a new rod jammed prevention plan was pr ovided.That was to set up a three stage impact pressure in the impact oil circuit.When the pressure of the high pressure water flushing was applied to discharge the drill ing cuttings, the water flushing pressure signal could be applied to control the on-off of the pushing cylinder and pilot oil circuit of the impactor in order to realize the aut 0 prevention of the slow rod jammed.A sudden down or up of the pushing pressure was applied to control the stop or impact of the impactor to prevent the rod jammed i n the karst cave.The rising of the rod rotary pressure was applied to control the backward of the pushing cylinder to prevent the slow rod jamming and crack rod jammin g.A relevant hydraulic control system was designed.The test results showed that the new hydraulic rod jamming prevention system could improve the rod jamming prev ention capacity of the drilling and loading machine and could realize the automatic prevention and different rod jamming handling.