Return tank capable of observing material inside

The utility model discloses a return tank capable of observing material inside. The return tank comprises a condensate inlet, a condensate outlet, a waste gas port and a tank body, wherein the condensate inlet and the condensate outlet are formed in the sidewall of the tank body, and the condensate inlet is higher than the condensate outlet; and a sight glass port with a sight glass is also formed in the sidewall of the tank body. According to the return tank capable of observing the material inside, the sight glass port with the sight glass is formed, the sight glass can be used for timely observing the return liquid in the return tank, the color and turbidity of the return liquid, and the rate of the condensate flowing from a condenser into the return tank, and thus the condensing efficiency of the condenser can be known, the problem of the overswelling of the return tank caused by discontinuous flowing of the return liquid in the top of a tower can be avoided, and the whole system can be effectively preven