The invention discloses a method to prepare perchlorate by electrolyzation. Make the electrobaths is greater than or equal to 3 in series become a group and arrange according to graded position difference, make the electrolyte flow from the high-position electrobath to the highest-position one, after electrolyzed, overflow into next one for electrolyzation, then overflow into next one, and electrolyzed in the final one to obtain the finished electrolyte, and control the conversion within 65-85%, to use the finished electrolyte to produce perchlorate product. It improves the current efficiency by above 15%, each ton of perchlorate can reduce electric consumption by 800kw.h, and the output of the perchlorate can be raised by 15% above.