The invention relates to a preparation and usage method of a water quality heavy metal detection agent. The preparation and usage method comprises the following steps: respectively weighing potassium hydroxide, potassium thiocyanate and polyvinylpyrrolidone at a mass ratio of (0.5-1):20:1, mixing and grinding to obtain a heavy metal detection powder I; weighing 4-(2-pyridylazo)-resorcinol, absolute ethyl alcohol, ammonium sulfate and ammonium chloride at a mass ratio of (0.02-0.1):10:100:100, dissolving 4-(2-pyridylazo)-resorcinol into absolute ethyl alcohol, evenly mixing with ammonium sulfate and ammonium chloride, drying, cooling and grinding to obtain a heavy metal detection powder II; adding 0.1-0.5g by mass of heavy metal detection powder I into 10ml a to-be-detected water sample, adding 0.2-0.8g by mass of heavy metal detection powder II after dissolution, standing for 10 minutes after dissolution, and measuring with a chromometer or a spectrophotometer, to obtain the concentration of heavy metals in the to-be-detected water sample. The preparation and usage method is high in sensitivity, the quality is stable, the carrying is convenient, the operation is simple, and the preparation and usage method is used for detecting the total amount of manganese (II), cobalt (II), nickel (II), copper (II), zinc (II), cadmium (II) and lead (II) in surface water, underground water, sea water, drinking water, industrial and agricultural water, and industrial waste water.