Bioactive calcium phosphate coatings on carbon/carbon composites were prepared by a cathode sonoelectrodepostion technique. The effects of electrodeposition time on the morphology, structure and composition of the coatings on carbon/carbon composites were investigated by SEM, EDAX, FTIR and XRD. The experimental results show that the plate-like crystals formed in initial stages of electrodeposition were identified to be CaHPO4.2H2O(DCPD). With the electrodeposition time elapsing, the formed needle-like precipitates were identified to be Ca10(PO4)6(OH)2(HA), the coating thickness and the n(Ca)/n(P) ratio increased continuously. The degree of crystallization of the coatings and the pH values of electrolyte decreased with the electrodeposition time increasing. The coatings were calcium-deficient apatite. In addition, the growth mechanism of coatings on C/C composites was also discussed.