In case of volcanic eruption, a robotic volcano exploration for observing restricted areas is expected to judge the evacuation call for inhabitants. An unmanned ground vehicle (UGV) is one possibility to apply to such exploration missions. When a UGV traverses on volcanic fields, a slippage between the vehicle and the terrain occurs. This is because the volcanic environment is covered with loose soil and rocks, and there are many slopes. The slippage causes several problems for UGVs, particularly localization and terrainability. Therefore, in this research, we propose a slip estimation method based on a slip model to apply to slip-compensated odometry for tracked vehicles. First, we propose a slip model for tracked vehicles based on the force acting on a robot on a slope. The proposed slip model has two parameters: a pitch angle dependence and a constant component, and these parameters were identified by indoor slope-traveling experiments. Next, we propose a slip parameter estimation method using a particle filter technique with a velocity measurement sensor, and report on the effectiveness of our method by slope-traveling experiments. The experimental result shows that the accuracy of our position estimation method based on the slip-compensated odometry is improved in comparison with conventional methods by using the slip parameters.