Characteristics of planar velocity distribution of vis-cous debris flow were analyzed using the measured data at Jiangjia Ravine,Yunnan,China. The velocity data were measured through using two radar velocimeters. The cross-sectional mean velocities were calculated and used to examine Kang et al’s(2004) relation-ship,which was established for converting the flow velocity at river centerline measured by a radar velocimeter into the mean velocity based on the stop-watch method. The velocity coefficient,K,defined by the ratio of the mean velocity to the maximum ve-locity,ranges from 0.2 to 0.6. Kang et al’s(2004) relationship was found being inapplicable to flows with K smaller than 0.43. This paper contributes to show the complexity of the planar velocity distribution of viscous debris flows and the applicability of Kang et al’s relationship. Characteristics of planar velocity distribution of vis-cous debris flow were analyzed using the measured data at Jiangjia Ravine, Yunnan, China. The velocity data were measured through using two radar velocimeters. The cross-sectional mean velocities were calculated and used to examine Kang et al’s (2004) relation-ship, which was established for converting the flow velocity at river centerline measured by a radar velocimeter into the mean velocity based on the stop-watch method. The velocity coefficient, K, defined by the ratio of the mean velocity Kang et al’s (2004) relationship was found inapplicable to flows with K smaller than 0.43. This paper contributes to show the complexity of the planar velocity distribution of viscous debris flows and the applicability of Kang et al’s relationship.