The author studied the estimation method of the fading zone where the remark signals disappear. These dead zones for the ramark navigation are caused by the interference between direct wave and sea-reflected that with phase difference of nπ So ; the distance may be estimated from the following formula well-known [numerical formula] where h_1 ; height of ramark antenna h_2 ; height of radar antenna d ; distance λ ; wave length The apparent height of antenna, howezer, is decreased influenced by the carvature of the earth in the long surface propagation. The author tried to estimate the distance and breadth of dead zone with effective heights in consideration of the distance effect. A practical sea experimental value is about 10% in distance and 2 or 3 times in breadth.