Objective Conventional ultrasonic measuring diameter and velocity of the vein to evaluate early venous tension changes of lower extremity deep vein thrombosis (DVT) with poor accuracy and repeatability. By applying the ratio cross-sectional perimeter2/cross-sectional area (C2/A) of common femoral vein(CFV), superficial femoral vein (SFV) and popliteal vein (POV) to evaluate DVT early vein tension change, discuss cut-off value method and diagnostic value of the C2/A preliminarily. Methods 150 patients in orthopedic without DVT underwent duplex ultrasound scan were studied. The value of venous flow velocity, Internal diameter, cross-sectional area(A), cross-sectional perimeter (C) and the ratio of C2/A of CFV, SFV and POV were recorded. The incidence of DVT were monitored by ultrasound after surgery and compared the value of the new parameter of C2/A before DVT occured. P<0.05 was considered statistically significant. Results There were significant differences in CFV inner diameter, CFV-C, CFV-A, CFV-C2/A, SFV-C, SFV-C2/A, POV-C, POV-A and POV-C2/A between the DVT group (24.70%) and the non-DVT group (75.30%) (all P<0.05). Area under curve (AUC) for CFV-C2/A, SFV-C2/A, and POV-C2/A as followed: 0.939 (95%CI: 0.888 -0.972, P<0.001), 0.937 (95%CI: 0.886 -0.970, P<0.001), and 0.917 (95%CI: 0.861-0.956, P<0.001), respectively; sensitivity 91.7%, 94.6%, and 91.9% , respectively; specificity 97.4%, 95.6%, and 93.8%, respectively. Conclusion The ratio of C2/A has high value in predicting thrombosis, and the interference factors are relatively less. It is providing new thinking and reference for intervention for clinical preventing DVT early.