The invention provides a device and a method for stabilizing relative positions of subarray gaps of seismic focus arrays in water. The device for stabilizing relative positions of the subarray gaps of the seismic focus arrays in water comprises traction rings mounted at the tails of subarray floating bodies of the seismic focus arrays, baseplate skeletons taking the shape of rings and spaced from the traction rings, baseplates being circular and disposed in the baseplate skeletons, and connecting columns connected between the baseplate skeletons and the traction rings. The method for stabilizing relative positions of the subarray gaps of the seismic focus arrays in water adopts the device for stabilizing relative positions of the subarray gaps of the seismic focus arrays in water, and comprises the step of connecting the traction rings to the tails of the subarray floating bodies of the seismic focus arrays through ropes. The device and method can increase the navigation resistance and reduce the influence of water flows on the floating bodies and subarrays, so that the offset of the tails of the floating bodies is within a certain control range and the subarray gaps can be controlled.