The invention provides a polyvinyl chloride hollow fiber composite nanofiltration membrane. The polyvinyl chloride hollow fiber composite nanofiltration membrane comprises a base membrane and an ultra-thin separation layer formed on the surface of the base membrane; the base membrane is a polyvinyl chloride hollow fiber microporous membrane; the ultra-thin separation layer is a polyamide layer; a preparation method comprises the following steps: step one, washing a base membrane assembly with deionized water, purging the inner surface of the base membrane with air, introducing a first polyamine solution into an inner cavity of the base membrane, and purging the inner surfaces of membrane yarns with air after amination; step two, introducing a second polyamine solution into the inner cavity of the base membrane, and purging the inner surfaces of membrane yarns with air after slight drainage; step three, introducing polyacyl chloride solution into a membrane inner cavity of the membrane assembly treated in the step one, the membrane assembly treated in the step two, or the membrane assembly treated in the step one and the step two, and airing in the air after reaction; step four, washing the membrane assembly which is subjected to interfacial polymerization treatment by taking polyamine as a water phase monomer and polyacyl chloride as an organic phase monomer with deionized water to obtain the polyvinyl chloride hollow fiber composite nanofiltration membrane showing positive charges; and the polyvinyl chloride hollow fiber composite nanofiltration membrane has a retention rate of above 95% for lead nitrate, magnesium sulfate, magnesium chloride and calcium chloride in water.