The invention discloses a dangerous chemical road transportation drainage basin water environment risk assessment method, which adopts an environment sensitive receptor influence derivation method, takes an environment sensitive receptor as an assessment basis, screens an environment risk road section according to the influence degree of dangerous chemical leakage to be transported on the environment sensitive receptor, and grades the environment risk road section; identifies a plurality of environmental risk road sections according to the drafted hazardous chemical substance transportation route, and then performs the environmental risk assessment and environmental risk grade division one by one on the road sections to serve as an auxiliary decision basis for finally determining a hazardous chemical substance transportation route scheme. The invention further discloses a dangerous chemical road transportation drainage basin water environment risk assessment system. An environment riskassessment module identifies an environment risk receptor around the leakage path, an environment risk source and environment risk substance information; the risk source identified by the environmentrisk identification sub-module is evaluated on the basis of an environment risk source evaluation method, the environment risk level of the risk source is evaluated, and the decision-making module isassisted to realize the prediction simulation of the sudden environment event.