To study the horizontal bearing characteristics of bridge pile foundations in the developed karst area with steep slope， the effects of slope changes on the ultimate bearing capacity of pile foundations， pile bending moment， and soil resistance on the pile side under the action of horizontal load on the pile foundations are investigated by using the centrifugal model test with the highway project as the basis， when the pile foundation thread through the karst cave and is located in the steep slope areas. The results show that the horizontal ultimate bearing capacity of the pile foundation decreases with the increasing foundation slope. For slopes less than 30°， the horizontal ultimate bearing capacity of the pile foundation is reduced by less than 10%， whereas for slopes greater than 30°， the horizontal ultimate bearing capacity of the pile foundation and the horizontal displacement of the pile top are significantly affected. The pile bending moment first increases gradually and then decreases gradually to zero along the direction of burial depth， and the decay rate is maximum in the embedded rock layer. The maximum value of the bending moment appears in the range of 2.5 to 5 times the pile diameter from the top of the pile. As the slope increases， the maximum value of the pile bending moment gradually increases and the position of the maximum bending moment gradually moves downwards. The soil resistance on the pile side increases and then decreases to zero along the depth of the pile foundation. The maximum soil resistance appears within 2.5 to 5 times the pile diameter from the pile top. With the increase of load， the depth of the maximum soil resistance of the pile side gradually moves down. The soil resistance on the pile side under different foundation slopes shows the small pattern in front of the pile and the large one behind the pile， and the difference in soil resistance is concentrated in the range of 2.5 to 5 times the pile diameter from the pile top.