Observation and measurement were conducted to investigate contact angle and its hysteresis on rough surface. The experimental results indicate that the increase in solid surface roughness enlarges advancing contact angle and decreases receding contact angle, resulting in enhanced hysteresis. It was observed that when Young's contact angle theta(Y) < 90degrees, as the roughness of solid surface increased the extent of the decrease in receding contact angle exceeded that of the increase in advancing contact angle. Based on the experimental observations, the concept of hysteresis tension was introduced to describe the contact angle hysteresis behavior on rough solid surface. The model provides a thoughtful understanding of the physical nature of contact angle hysteresis, in particular an instructive description of the influence of surface roughness on the hysteresis. The prediction of the model is found in quite good agreement with the experimental observation and measurement.