The invention provides a rotary drilling rig, a mast hydraulic control system and a mast lifting up/ down control method. The mast hydraulic control system comprises a left mast oil cylinder, a right mast oil cylinder, a jacking oil cylinder, a first reversing valve which is connected with the left mast oil cylinder, a second reversing valve which is connected with the right mast oil cylinder, a third reversing valve which is connected with the jacking oil cylinder, a left mast balancing valve, a right mast balancing valve, a jacking balancing valve, a first switching valve which is connected in parallel with the left mast balancing valve, a second switching valve which is connected in parallel with the right mast balancing valve, and a third switching valve which is connected between a head port of the jacking oil cylinder and the third reversing valve, wherein the third switching valve is provided with a connecting throttling position and a stopping position; when the third switching valve is at the connecting throttling position, oil in the head port of the jacking oil cylinder can slowly return through the connected third switching valve and a fifth pipeline. According to the mast hydraulic control system, a rear lying type big triangular mast lifting up/ down hydraulic control system is adopted, so that the convenience of maintenance, mounting and dismounting is ensured, and moreover, the rock embedding stability is high.