[Objective] This study aimed to investigate the translation and rotation of healthy elbow joints during active flexion and extension, to understand the kinematic characteristics of the healthy elbow joint, and to provide baseline data for the treatment of elbow instability and injury. [Methods] Ten healthy subjects with no history of upper extremity trauma were recruited. We applied dual fluoroscopic tracking technique to quantify six-degree-of-freedom (6-DOF) kinematics of humeroulnar and humeroradial joint from full extension to maximum flexion in supination position. Correlation analysis was used to evaluate the relationship between the 6-DOF kinematics of the elbow joint. [Results] During the elbow active flexion and extension motion, valgus angle of humeroulnar joint gradually decreased from 15.2°±3.1° to 5.3°±2.3°while the flexion increasing. valgus angle of humeroradical joint gradually decreased from 19.7°±4.2° to 8.2°±2.4° from full extension to maximum flexion. The valgus angle of humeroulnar and humeroradial joint are linearly related to the flexion angle during the flexion and extension motion (R2=0.98, p<0.0001, R2=0.989, p<0.0001）. The internal rotation of humeroulnar joint is quadratic nonlinearly related to the flexion angle during motion (R2=0.93, p<0.0001）. The maximum internal rotation of the ulnar was 4.0°±4.9° at 110° flexion, and the maximum externally rotation was 5.1°±4.2° as follow. The internal rotation of humeroulnar joint is gradually increased from 3.2°±16.0° to 27.2°±18.0°. [Conclusions] Humeroulnar joint decreases linearly at valgus change, it shows nonlinearly change which rotate internally firstly and then rotate externally during flexion. The valgus angle of humeroradial joint decrease linearly and internal rotation angle increase linearly. Therefore, humeroulnar joint is not a hinge joint during flexion. Kinematic is difference between humeroulnar and humeroracial joint. The current study provided insights into clinical treatment of complex elbow injuries, elbow instability, and development of new elbow prosthesis.