Abstract: The problem discussed in this article is the disposal of waste chromic acid solution produced from the plastic roughing by diaphragm electrolysis in which the diaphragm is used as the cation exchange membrane. On the conditiorr that the temperature is at 40—50℃, the applied voltage is 2.5—3.0 V, and the least value of Cr³⁺+ is controlled at 10g/L, the current density is 3.5—4.0A/dm², the current efficiency reaches 72%—80% and the electric energy consumption is only 150—170 kW·h/m3. The new technique has a great advantage over the ceramic diaphragm electrolysis.