Many researchers pay their attentions to the biostability of drinking water more and more. Biodegradable dissolved organic carbon can provide a good indicator for biostability of drinking water in distribution-system. The main objective of this study was to research the regulations of concentration changes of biodegradable dissolved organic carbon and the populations of the total bacteria in water distribution-system of a city in china. The field experiments showed that the values of biodegradable dissolved organic carbon decreased along the main pipes in the water distribution-system, and the rate of the decrease was lower in the front part of the two main pipes than in the back part. At the same time, the populations of the total bacteria increased in the front part of the NO.1 main pipe and decreased in the back part. Our research provided the theoretical foundation for limiting the bacteria regrowth and to ensure the biostability of drinking water.