The invention relates to the technical field of sensors, and specifically relates to a preparation method of an electrode and an electrochemical sensor and an application thereof. The invention provides the preparation method of the electrode on the one hand, and the method comprises the following steps of mixing a conductive carbon paste, a conductive material and a functional material to obtaina composite conductive carbon paste, and preparing the electrode through the composite conductive carbon paste; the mass ratio of the functional material to the conductive material is 1:1 to 10:1; andthe sum of the mass of the functional material and the conductive material accounts for 10% to 30% of the mass of the composite conductive carbon paste. The electrode surface does not need to be further modified, can be repeatable, the preparation process is simple and the electrode can be produced in bulk. The electrochemical sensor provided by the invention can carry out high-sensitivity and efficient detection on pentachlorophenol, and conductive materials in the composite conductive carbon paste reduces the resistance of the carbon paste, and the electron transport rate of the electrode is increased; and materials capable of responding to the pentachlorophenol in the carbon slurry can improve the detection sensitivity and improve the selectivity of the sensor.