The utility model discloses a height-adjustable crop straw compression chamber which comprises a compression chamber body, a piston arranged in the compression chamber body in a sliding mode, a pistondriving mechanism, a height adjusting mechanism and a posture keeping structure. The compression chamber comprises an upper plate, a lower plate, a left side structure and a right side structure, andwhen the upper plate and the lower plate move relatively, the left side and the right side of the compression chamber are closed through the left side structure and the right side structure; the height adjusting mechanism is used for adjusting the height of the upper plate and/or the lower plate; the piston comprises a fixed piston and a movable piston which are elastically connected, the movablepiston can elastically stretch up and down relative to the fixed piston along with movement of the upper plate and/or the lower plate, and the piston driving mechanism is used for driving the fixed piston to slide; when the posture maintaining structure enables the fixed piston and the movable piston to stretch out and draw back relatively, the fixed piston and the movable piston only translate relatively and do not rotate relatively. The straw baler can be used for crop straw baling tests, the height of the compression chamber most suitable for crop straw baling operation is obtained according to different straw types, and the application range is wide.