To further clarify possible sports injury of shoulder joint of excellent discus athletes at beginning phase of rotation and biomechanic characteristics demonstrated, the paper adopts close range dynamic stereo photography measurement method for fixed-point shooting of live competition, training of discus athletes. Comprehensive analysis and research of motion image and information is done with professional video, finally biomechanical indexes of athletes are obtained, and in-depth inquiry is done for possible sports injury of shoulder joint at beginning phase of rotation and biomechanical characteristics demonstrated. Results show that the highest constituent ratio of shoulder joint injury of excellent discus athletes comes from injury of tendon of long head of biceps brachii, followed by rotator cuff injury, acromioclavicular joint sprain and dislocation, dislocation and subluxation (glenohumeral joint), deltoid muscle strain. Biomechanical results show that biomechanical indexes of shoulder joint at beginning phase of rotation are as follows: right from the moment of lifting of right foot, shoulder and hip angle is 45 degrees, pulling angle is 126 degrees, shoulder axis angle is 2 degrees, velocity of left shoulder is 2.64 m/s, velocity of right shoulder is 0.95m/s; right from the moment of lifting of left foot, shoulder and hip angle is 27 degrees, pulling angle is 150 degrees, shoulder axis angle is -12 degrees, speed of left shoulder is 1.96 m/s, speed of right shoulder is 1.97 m/s. In conclusion, at beginning phase of rotation, increased pulling angle caused the highest ratio of injury of tendon of long head of biceps brachii. Therefore, in the daily training and competition, adjusting of corresponding angle should be a focus.