Abstract: Objective Measuring the displacement and deformation of the fifth screw under different tensile force before or after adultal internal fixation with compressing steel plate for femoral fractuer by digital speckle correlation method.And analysis of the displacement and deformation after reducing the number of screws.Aimed at providing a theoretical basis for clinical femoral internal fixation with compressing steel plate about the number of screws. Methods Taking the antisepsis femoral specimen of grown-ups, embedding and fixing with tooth powder after removing the soft tissue, producing a fixed model in the 1/2 femur.Fixing steel plate below the lateral femur subperiosteal with five screws through the fourth floor of cortical bone on both sides of the fractures, samples were divided into 10 states, group A-J were measured by orders, under the rally of 400 N,500N , measuring the displayment of the fifth screw with CSS-44100-e-universal test machine for loading rally experiment ,and automatic data processing. Results For analysis of variance, the mean displacement measurements of the fifth screw under rally of 400N,500N, B-J group and A group have significant differences（EM>P/EM><0.05）.The mean deformation measurements of the fifth screw - under rally of 400N,500N, group A and group F-J group have significant differences（EM>P/EM><0.05）; group A and B-E group have no significant differences.Conclusion In a certain range, the fracture displacement and the numuber of the screws show negative correlation. The screws near the fracture line for femoral compression plate internal fixation of femoral fractuer is easily broken because

Key words: Shaft of femur, Fracture, Internal fixation with compressing steel plate, Biomechanics, Human