Preparation processes of fibrous monolithic ceramics in-situ synthesized is a simple and cheap way to make ceramics with high performance. In this paper, the process of in-situ synthesizing Si3N4 fibrous monolithic ceramics and the main factors which affect properties of the material were investigated in detail. It is found that the reinforcing effect comes from the synergism of the toughening in two different scale. One is the oriented growth of grains or oriented distribution of whiskers in the fibrous cells. The other is the effect of the special fibrous monolithic structure formed by the weak interfaces between fibrous cells. The results showed that the fractural toughness of the fibrous monolithic ceramics can reach 23.95 MPa.m(1/2) at room temperature.