The utility model discloses a pumping unit speed reducing box inner washing and oil adding device. Quick washing and oil adding can be achieved on a speed reducing box. Working efficiency can be improved. The speed reducing box inner washing and oil adding device comprises an internal combustion engine and a screw pump which are connected through a belt wheel and a belt. A sucking-in opening of the screw pump is communicated with a sucking-in manifold. A discharging opening of the screw pump is communicated with a discharging manifold. The problem that currently, the numbers of devices and personnel used for washing a speed reducing box are large is solved, the number of needed working personnel is small, meanwhile, the labor intensity of the operation personnel is lowered, and great using effect and economical effect are achieved.