The invention discloses a method for determining the minimum buried depth of an underwater tunnel. The method comprises the steps that the influences of a reinforcing scheme in the designing process of the underwater tunnel and a construction segment partition scheme in the construction process on the tunnel buried depth are considered; firstly, the vertical section of the tunnel is preliminarilydetermined according to the wiring conditions at the two ends of an underwater tunnel project and the route slope, then a crucial section of the tunnel is selected, the crucial section under the condition that reinforcement is conducted is calculated, and therefore the minimum buried depth of tunnel construction safety is ensured; and meanwhile the water seepage amount in the operational period after the tunnel is reinforced is calculated, and when the water seepage amount obtained through calculation is smaller than a water seepage amount control standard in the tunnel operational period, thedetermined buried depth is the minimum buried depth of the tunnel. When the minimum buried depth of the tunnel is determined, all crucial sections of the whole tunnel all need to meet the requirements of the minimum buried depth, and the method can further appropriately reduce the project construction cost under the premise that the tunnel construction safety is ensured.