Provided are a controllable pressure jetting apparatus based on a hydraulic energy accumulator and a jetting method. The jetting apparatus comprises a pressure storage system, a pressure holding system, a sealing system and an injection system. The pressure storage system comprises a front half (4-2) of a pressure cylinder, an annular piston (5) and a middle connection body (7). The pressure holding system comprises an energy accumulator (2), a rear half (4-1) of a pressure cylinder, and a rear end cover (1). The sealing system comprises a hydraulic propulsion cylinder (8), a propulsion piston (9), a front end cover (10), a sealing tube (12), a thickened end part (14) and an expanding rubber tube (13). The jetting system comprises a hydraulic valve body (6) and a jetting gun tube (11). The jetting apparatus can quickly apply pressure to the bottom of a drilling hole in a hydraulic manner, so that rock is broken under tension, thereby improving the excavating efficiency of hard rock.