The invention discloses a system and a method for determining the environment traffic capacity of an expressway based on vehicle emission. The system comprises a data acquisition system, a processor, a display and a server, wherein the processor is used for analyzing and processing data which are acquired by the data acquisition system; the display and the server are connected with the processor; the processor is in wireless connection and communication with the data acquisition system through a wireless communication system; and the data acquisition system consists of meteorological parameter detection equipment, traffic flow detection equipment and pollutant concentration detection equipment. The method comprises the following steps of: 1, acquisition and real-time uploading of the data; 2, determination of the environment traffic capacity of the expressway: determination of the cumulated amount of various vehicle emission pollutants, determination of a dilution factor f, and determination of the environment traffic capacity of a road section j of the expressway; and 3, synchronous output and storage of a processing result. The invention has the advantages of novel and reasonable design, convenience for implementation, high real-time performance, high determination accuracy of the environment traffic capacity of the expressway, high reliability, high practicability and high popularization and application value.