The invention relates to a method for preparing a polypyrrole/chitosan composite electrode. The method comprises the following steps: composite material preparation, grinding and charging, and hot pressing. The pyrrole with favorable conductivity and chitosan with favorable adsorbability are compounded together, so that the composite electrode has favorable electrode activity. The added activated carbon is used as a conducting agent, so that the mechanical properties and electrochemical properties of the composite electrode are obviously enhanced. In the electrode preparation process, no adhesive is added, and the temperature, pressure, time and conditions for hot pressing are controlled to obtain the polymer composite electrode with excellent properties. The composite electrode has the advantages of electrochemical properties, low cost, environment friendliness and favorable cycle performance, and can be used for treating heavy metal wastewater by capacitive deionization (CDI).