In thins paper are inqestigated 124—cubic graph and 115—cubic graphs. It is showo that taere exists one and only one 124—cubic graph shown in Fig. 6. We define the fundamental block of 115—cubic graphs as the graph that is isomorphic to the graph shown in Fig

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The action of replacing edges of the perfect matching in a even cycle by the fundamental block of 115—cubic graphs is called fundamental block replacement of this even cycle and then prove that every 115—cubic graph can be obtained by means of its funaamental block replacement of an even cycle.