The invention relates to a high-density polyethylene (HDPE) mother solution deactivation technology. The technology comprises the following steps: (1) injecting alkali liquid or water into a conveyingpipeline of an HDPE mother solution from the upstream; conveying the HDPE mother solution added with the water or the alkali liquid into a mixer; (2) sufficiently mixing under the stirring of an axial flow blade of the mixer so as to deactivate a catalyst in the HDPE mother solution and obtain a catalyst deactivated HDPE mother solution; (3) pressurizing the catalyst deactivated HDPE mother solution under the action of a centrifugal blade of the mixer and then conveying the solution into a separation tank; separating the solution under the action of low-pressure steam through controlling a pressure differential type liquid level transmitter I and a pressure differential type liquid level transmitter II, so as to obtain volatile matters, a separated HDPE mother solution, separated water oralkali liquid and steam condensate; after carrying out secondary condensation on the volatile matters, enabling the volatile matters to reflow into the separation tank; discharging the separated water or alkali liquid into a water treatment system; conveying the steam condensate into a condensate pipeline; conveying the separated HDPE mother solution into a subsequent section. The method providedby the invention is simple and easy to implement.