The work aims to explore influence law of coating growth on its micro-hardness and determine the best time of preparing high-hardness micro-arc oxide coating by establishing dynamic relationship between oxidation time and coating growth of ZrO2/TiO2 composite ceramic coating. Micro-arc oxidation was performed to TC4 for different time provided with zirconium salt system and optimized electrical parameters to analyze coating surface and cross-section morphology, elements distribution and phase composition, measure and analyze microhardness and porosity of the coating. The coating growth exhibited different dynamic characteristics and macroscopic appearance in the test oxidation time. There were two stages during the coating growth: the coating thickness increased linearly in the first stage, and then growth rate slowed down in the second stage. The surface porosity increased over time. The hardness was the highest when the oxidization has last for 15 min. And the micro-hardness first increased and then decreased over time. The main factors influencing microhardness of MAO coating are phase composition and surface structure. The micro-hardness increases linearly as coating thickness exhibits linear growth; and the micro-hardness decreases as coating thickness exhibits slow growth.