The invention discloses a user-based demarcating method and a sample collecting system of a water nephelometer, effectively solving the technical difficulty that the prior water turbidness numerical value deviates from the water aerosol concentration numerical value. The user-based demarcating method is characterized in that a specific water sample in a water body from a preset user of a nephelometer is taken as standard liquid for demarcating the nephelometer; the collected specific water sample is divided into an A part and a B part, and because the aerosol concentration of the water sampleA and the water sample B is equal, when the aerosol concentration of the water sample B is detected by the sample collecting system and a collecting device, the water sample A becomes the standard liquid with known aerosol concentration. The water sample A is put in the electronic nephelometer to be demarcated, and the ratio of the scattered light intensity and incident light intensity or the transmitted light intensity and the incident light intensity of the electronic nephelometer is measured, is converted into digital numbers equivalent to the aerosol concentration of the water sample A, and is conveniently and accurately displayed on a display screen of the nephelometer.