The behavior of SiC coating in carbon fiber reinforced aluminum, metal coatings, Ni, Fe in carbon fiber reinforced copper and alumina coated $K_2O{cdot}6TiO_2$ whisker reinforced aluminum composites were investigated, respectively, by modern devices, like TEM, SEM etc. with the goal of controlling the interfacial interaction and wettability of reinforcement, like carbon fibers, $K_2O{cdot}6TiO_2$ whiskers with matrices. SiC coating produced by a polycarbosilane solution process improved effectively the strength because it successfully resisted the oxidation of carbon fibers themselves and the harmful reaction between carbon fibers and molten aluminum during fabrication process and heating process of the composites. The metal coating, Fe and Ni by electrical plating, strengthened the bonding of carbon fibers with copper, by changing the bonding state of the interface from mechanical one to partly chemical one. Therefore the strengths of composites were improved obviously. The aluminal coating on $K_2O{cdot}6TiO_2$ alos controlled the diffusion of K element from whiskers into aluminum matrix and reaction with aluminum and led the optimaization of interfacial bonding between the whiskers and aluminum, so that the properties of the composites reached a higher level.