The invention relates to the technical field of analysis and detection and in particular to a preparation method of a benzenediol electrochemical sensor based on sodium hydroxide as well as a detection method. The electrochemical sensor can realize sensitive, quick and simultaneous detection on three benzenediol isomers, and a detection limit is as low as 0.01[mu]m. The preparation method comprises the following steps: polishing a bare glass carbon electrode on deerskin with Al2O3 powder until a mirror surface is formed, then sequentially performing ultrasonic treatment for 5 minutes in acetone, HNO3 and redistilled water, placing a prepared electrode in K3[Fe(CN)6] solution, testing by adopting a cyclic voltammetry method, performing the next step if potential difference is within 80mV, otherwise repeating the steps, placing the electrode tested to be qualified into NaOH solution, performing electrodeposition by virtue of a chronopotentiometry method under the conditions that a constant current is 0.1-0.5mA and deposition time is 20-300s, then washing the electrode with distilled water, and performing detection by adopting a certain detection method.