The invention provides an adjustable drilling device in the hydraulic direction of a coal seam. The device comprises a spraying nozzle, a middle joint, a water inlet joint and rotary connection assemblies; the water outlet end of the middle joint is fixedly connected with the spraying nozzle, the end surface of the inlet end of the middle joint sinks to form a spherical groove, the outlet end of the water inlet joint is of a spherical structure and is embedded in the spherical groove, and the middle joint and the water inlet joint can rotate oppositely; the water inlet joint is coaxially provided with a main water inlet passage, the water inlet joint is provided with four direction adjusting passages, and the direction adjusting passages are uniformly arranged in the circumferential direction of the main water inlet passage; four limiting grooves are formed in the spherical surface of the water outlet end of the water inlet joint, the direction adjusting passages are communicated withthe limit grooves, and the side wall of the spherical groove of the intermediate joint is provided with four direction adjusting water outlet holes; the rotary connection assemblies are arranged in the limit groove and the direction adjusting water outlet holes; the hole forming efficiency of bunch holes is improved.