The utility model provides a septic tank that contains interior strengthening rib, including main part, solid fixed ring, internal fixation piece and external fixation piece, the inside of main part is provided with solid fixed ring, the internal surface of main part is opened there is the guiding gutter, the front end of main part is provided with preceding fixed plate, the top of preceding fixed plate is provided with the internal fixation piece, it has preceding fixed orifices to open on the preceding fixed plate, the rear end of main part is provided with the after -fixing board, it has the after -fixing hole to open on the after -fixing board, the below of after -fixing board is provided with the external fixation piece, compared with the prior art, the utility model discloses following beneficial effect has: the pollution in various degree of effectively solving seepage that traditional brick mixed the septic tank, causing underground water source and cause the slope scheduling problem to the building to can carry out follow -up advanced treatment for the sewage to discharging and establish the basis, gu fixed ring's existence has increased the stability of main part.