Abstract: In order to estimate position and orientation of object,an EKF method based on dual quaternion from monocular camera was investigated.An improved EKF method based on James method was proposed.In the EKF,relative translation and rotation second derivations of the object were added as state assignment.Object lines are measured variables,which were transformed between coordinate frames by dual quaternion.Corresponding system model and measurement model were deduced.At the same time,some mistakes in James method were rectified.Experiment tests using turntable to demonstrate relative motion and position were done.Actual experimental data of rotation at a constant speed of 20 /s show that the improved method get almost the same precision of pose estimation as James method.While actual experimental data of 40 /s show that the improved method can get better precision and robustness.