The invention discloses a preparation method of a biosensor and a modified electrode that take the substrate of attapulgite clay, the sensor takes the substrate of the attapulgite clay with a natural nano structure, utilizes the unique pore canal structure and the excellent adsorptive power of the attapulgite clay, fixes glucose oxidase (GOD) on the surface of the attapulgite clay, coats the attapulgite clay with adsorbed oxidase on the surface of a glassy carbon electrode, and drops and coats a layer of Nafion methanol solution on the surface, thus forming the Nafion-GOD / ATP / GC modified electrode. The modified electrode, a platinum sheet electrode, a saturated calomel electrode form an electrolytic cell, which is further connected with a converter and a display screen into the biosensor. The biosensor has quick response time, high sensitivity, simple and convenient production method, good repeatability and stability, and convenient mechanization, integration and commercialization.