The invention relates to pressure adjusting devices for water conservancy pipelines and discloses an internal water pressure adjusting device for a water conservancy pipeline. According to the internal water pressure adjusting device for the water conservancy pipeline, after a piston moves to buffer the water pressure, discharging pressure relief is conducted. The internal water pressure adjustingdevice is characterized in that a connecting sleeve is arranged at one end of a main cylinder in a sleeving mode; a sliding groove and a through hole are formed in the outer side of the main cylinder, and the through hole is located above the sliding groove; a through hole is formed in the middle of the other end of the main cylinder; a thread is arranged on the inner wall of the main cylinder; astrip-shaped groove is formed in the inner wall of the main cylinder; one end of a connecting cylinder is arranged on the main cylinder and corresponds to the through hole in one end of the main cylinder; a through hole is formed in the connecting cylinder; a fixed sleeve is arranged at the other end of the connecting cylinder in a sleeving mode; one end of an adjusting rotary knob penetrates through the through hole in the other end of the main cylinder to be arranged in the main cylinder; a thread sleeve is arranged in the main cylinder; a thread is arranged on the outer wall of the threadsleeve and matched with the thread on the inner wall of the main cylinder; and an annular groove is formed in the thread sleeve, and a rotating sleeve is arranged in the thread sleeve and connected with the thread sleeve.