The invention relates to a preparing method of silicon-carbon-nitrogen (SiCN) wave absorbing ceramic base composite materials. The preparing method includes: adopting chemical vapor deposition (CAD) or chemical vapor infiltration (CAI) technology, using SiC14, SiHC13 or other chlorine silicon compounds or silicane as a silicon source, using CH4, C3H6, C2H2 or other alkane, olefin or alkyne as a carbon source, using NH3 or N2 as a nitrogen source, using H2 as a carrier gas and a reaction gas, using argon as a diluting gas, synthesizing SiCN on substrate materials in situ, and obtaining a SiCN matrix and a coating which are uniform and compact, without impurities, and with devisable compositions and wave absorbing properties. The preparing method overcomes the shortcoming that CFCC-SiC prepared by adopting the prior art is insufficient in wave absorbing performance, and simultaneously facilitates achieving control of compositions, permeability, thickness and wave absorbing performance of a wave absorbing matrix.