To establish an early-warning system for source water pollution accident, a membrane inlet / time-of-flight mass spectrometry technology was applied to a series of pollution scenarios as an online monitoring method for typical volatile organic compounds such as BTEX (benzene, toluene, ethylbenzene and xylene), substituted benzenes, and halogenated aliphatic hydrocarbons. It was shown that this technology can adequately meet the requirements of realtime analysis with short response time to the target organic pollutants (30～70 s for BTEX and 30 s for halogenated aliphatic hydrocarbons) in a linear detecting range of 3～4 magnitudes; the detection limits of BTEX and chlorobenzene were less than 10 μg·L-1. The results of 52 simulated water pollution accidents in a 30-days’ continuous monitoring indicated that the monitoring system was stable with the relative standard deviation less than 5%; the accuracy was acceptable and could be reduced to within 10% by periodical calibrations. Membrane inlet/time-of-flight mass spectrometry technology was proven to be available for the remote monitoring and early-warning of source water pollution accident.