A lateral pull rod mechanism configured to lock a steel tube support assembly, comprising a pull rod (201), an upper connecting plate (208), a pull rod through hole (202) provided on the upper connecting plate (208), a lower connecting plate (209), a lower lateral pull rod clamping groove (210) provided on the lower connecting plate (209), a middle connecting block (211) disposed between the upper connecting plate (208) and the lower connecting plate (209), a middle lateral pull rod clamping groove (212) provided on the middle connecting block (211), a threaded section (203) provided at the upper end of the pull rod (201), a fastening nut (204) in screwed connection with the threaded section (203), an anti-disengaging portion (205) disposed at the lower end of the pull rod (201) and configured to prevent the pull rod (201) from vertically disengaging from the lower lateral pull rod clamping groove (210), and a lateral stopping plate (206) configured to prevent the anti-disengaging portion (205) from sliding outwards.