As the first step of the fire/gas-detection systems of floating production storage and offloading (FPSO) units is to iden-tify leakage accidents, gas detectors play an important role in controlling the leakage risk. To improve the leakage scenario detection rate and reduce the cumulative risk value, this paper presents an optimization method of the gas detector placement. The probability density distribution and cumulative probability density distribution of the leakage source variables and environmental variables were calculated based on the Offshore Reliability Data and the statistical data of the relevant leakage variables. A potential leakage sce-nario set was constructed using Latin hypercube sampling. The typical FPSO leakage scenarios were analyzed through computational fluid dynamics (CFD), and the impacts of different parameters on the leakage were addressed. A series of detectors was deployed according to the simulation results. The minimization of the product of effective detection time and gas leakage volume was the risk optimization objective, and the location and number of detectors were taken as decision variables. A greedy extraction heuristic algo-rithm was used to solve the optimization problem. The results show that the optimized placement had a better monitoring effect on the leakage scenario.