The influences of shape characteristics and pressure on n-Heptane ring fire were investigated through two groups of experiments. In group A, the ring fire with varying shape characteristics was conducted. In group B, the ring fire was performed under sub-atmospheric pressures including 45 kPa, 60 kPa, 75 kPa, and 90 kPa. The results show that the mass loss rate is determined by combined results of air entrainment and heat dissipation effect. The flame structure is divided into merged flame and separated flame. The axis temperature has no significant difference in growth stage but presents a corresponding relationship in decrease stage.