In this article, we propose a multi-staged algorithm to detect the magnitude, direction and location of a single external force applied to a humanoid robot while performing dynamic tasks. We use contact force and joint torque sensors as well as IMU to estimate accelerations and build the equation of motion. Then using a search process and based on Jacobian decomposition, we analytically find the point on the whole body which can best account for the error observed in the equation of motion. The method can provide reasonably stable and consistent estimations, even during fast dynamic motions.