Abstract: Based on the BWRS state equation, the complete formula for calculation Joule-Thomson coefficient is derived, and the detail calculation procedure is given. The examples show that BWRS method is available at single component hydrocarbon gas, single component non-hydrocarbon gas, and the natural gas made up of hydrocarbon component and non-hydrocarbon component. Compared with LKP and SRK methods, BWRS method is simpler and higher precision. The BWRS method in the essay provides the theory base for the throttle temperature drop calculation in natural gas transmitted by pipeline and lighter hydrocarbon recovery.