Rectangular solid control systems are characterized by simple structure and attractive appearances. There are drilling fluid tanks with two specifications of 10m and 12m respectively to meet demands of different clients. Inclined bottom structures of the tank bottom on seating can facilitate removal of fluids and sand accumulated. The tank shall be made of pre-fabricated corrugated steel plates. With rational flow design, these systems can ensure proper performances related to preparation, weighting, screening, circulating, control and storage of drilling fluids.