The present investigation mainly focuses on effects of centrifugal forces and casting modulus on structures and mechanical properties of Ti-6Al-4V alloy formed under different vertical centrifugal casting conditions in graphite molds. Mold rotating rates of 0, 110 and 210 rpm are considered with experimental method. Results show that, grain size and lamellar thickness decrease with the decreasing of modulus or increasing of centrifugal force, and tensile strengths are considerably enhanced with the decreasing of modulus or increasing of centrifugal force, but the elongation shows the opposite changing trend. The quantitative relationships among gravity coefficient, casting modulus and structures or mechanical properties of Ti-6Al-4V alloy have been obtained. As the comparison of Ti-6Al-4V alloy cast in graphite mold under gravity field, the structures of steeped casting in metal mold are also investigated. It was found that the grain size or lamellar thickness in both two molds shows the same changing trend with the cooling rate, and the quantitative relationships between structures and cooling rates have been obtained.