The invention discloses an improved buried sewage disposal system which comprises a shell. An inspection port communicating to the inner part of the shell is formed in the top wall of the shell, a liner of a hollow structure is arranged in the shell, the liner is supported on the bottom wall of the shell through a ball cup, a purification pond is arranged in the liner, the purification pond is connected to a water inlet pipe and a water outlet pipe, and the far ends of the water inlet pipe and the water outlet pipe pass through the outer wall of the shell; at least two lifting mechanisms are symmetrically arranged on the outer side of the liner in the shell for adjusting the levelness of the liner. By adopting the structure, when the shell inclines, the liner can be strengthened through the inner liner, so that purification equipment in the purification pond can be substantially kept horizontal all the way and can be kept in normal work, so that the working reliability and the stability of the sewage disposal device are improved. Meanwhile, the air quality in the shell is improved, so that a safe and proper operating environment is provided for staff.