The research on oil-gas leak from the central drain pipe of floating-roof tank is of great significance for the timely formulation of reasonable emergency measures and the prevention of major accidents. A method for judging the leak of the central drain pipe was introduced. The influence of different leak locations on the alarm time after the leak of central drain pipe was analyzed through the numerical simulation. The simulation showed that the maximum difference between alarm times of the three leak locations was 1 308 s, which meant that the leak location had a greater impact on the alarm time. The feasibility of laser detection of oil-gas leak in central drain pipe was verified by using CH4 with a concentration of 10% instead of the oil-gas. The results show that the tunable diode laser absorption spectroscopy (TDLAS) technology can be used to detect the oil-gas concentration in the leak alarm system of central drain pipe, which provides a certain reference meaning for the design of the leak alarm system of central drain pipe of floating-roof tank.