An elevation-adjustable display screen support arm includes arm shaft with box-like shaft body, balance adjustment mechanism accommodated in box-like shaft body and including gear train, first sliding tooth rack, second sliding tooth rack and tension spring, and display screen mounting head including body block, first guideway, second guideway and connection panel. When adjusting the elevation of the supported display screen, body block is driven to move first sliding tooth rack in rotating gear train, causing gear train to move second sliding tooth rack in driving actuating plate to stretch or compress tension spring, and thus, rotation of gear train causes tension spring to provide a corresponding torque that is acted upon first sliding tooth rack to control upward or downward movement of display screen mounting head and supported display screen in stepless manner.