Abstract: In order to get passenger flow size and characteristics in Guangzhou-Shenzhen railway, the paper studies passenger flow forecast issue.Firstly, the Gray Forecast Model is applied to the calculation of GDP, population and employee number in traffic district along the railway.Secondly, after careful analysis of the four-step traffic forecast method, the author calculates the amount of passenger flow generation and attraction, passenger flow distribution and passenger flow proportion.At last, the forecast result of passenger flow(2020 and 2030) is worked out.The forecast data can be used to design a new passenger train operation plan.