The invention discloses a preparation method of vanadic acid copper. The preparation method comprises the steps that firstly, by the adoption of the direct current electrolysis mode, vanadic acid copper precursors of different structures and with different particle sizes are prepared by controlling the current density, electrolyte concentration and temperature; then products obtained in anode liquor are collected, filtered, washed and dried; and finally, the temperature is increased to 400-600 DEG C at the speed of 2-5 DEG C/min in the air atmosphere, high-temperature roasting is conducted for 3-5 h, and the high-purity and high-cleanliness vanadic acid copper is obtained, specifically, the structural composition of the vanadic acid copper is Cu<3>(VO<4>)<2>. According to the preparation method, by controlling the corresponding conditions, main morphological structures of the obtained product are spherical particles and micron rod-like structures.