Ceramic-like coatings were formed using alternate ultra-narrow pulse microarc oxidation method on alloy Ti6Al4V in Na2SiO3-KOH-(NaPO3)6 aqueous solution. A constant voltage (U=500 V) regime of microarc oxidation was applied to reveal the effect of positive pulse duty cycle on their growth rate, microstructure and phase composition. In order to obtain the optimum process, a constant current density (J=60 mA/cm2) regime combined with the stepped adjusting of positive duty cycle during microarc oxidation process is also proposed. With the positive duty cycle increasing from 4 % to 20 %, the growth rate of the coatings increases and the surface morphology becomes coarser. The as-deposited coatings are mainly composed of anatase and rutile TiO2. With the pulse duration increasing, the content of anatase decreases, while rutile increases and becomes the predominant phase. Considering the microstructure and growing thickness of the coatings, 8 % of positive duty cycle is suitable. When applying the constant current density regime, the growth rate of coatings is significantly increased compared with that by the constant voltage regime. And the morphology of the coatings is obviously improved by using the stepped adjusting of duty cycle furthermore.