Abstract: Based on the reactive fame spray technique , TiC- TiB₂ multiphase coatings were prepared on the steelsubst rate with Ti-B₄C-C reactant s. By elect ronic microcosmic observation , X-ray diff raction and energy spect rumanalysis , the st ructure and it s forming causes of TiC- TiB₂ multiphase coatings were discussed. The result s showthat the coatings have the multiphase heterogeneous metastable st ructure , which have no conspicuous layer-shapedst ructure that the t raditional flame spray coatings have. The coatings are composed of the major phases TiC_0.7N_0.3 ,TiC_0.2N_0.8 , TiB₂ , a little of TiO₂ , Ti₂O , Ti₃O₅ and some pores. There are three kinds of st ructures with differentcharacteristics in the coatings the cluster-shaped st ructure in micron-nanometer size , the 1～3μm st ructure takingon equiaxed particles dist ribution , and the deep black pores. Before meeting the subst rate the spray particles combust , react , and form molten ceramic beads (in solid and hollow two kinds) or abnormal ceramic granules (having thesame figure as the spray particles) . Af ter colliding with the subst rate , they distort , cool , quickly crystallize andform the three kinds of st ructures.