Objectives: three-dimensional color doppler was used to evaluate the true umbilical cord knot. Methods: study 2 case clinical diagnosis case, analysis three-dimensional color doppler images, compare the image characteristic between true umbilical cord knot and false umbilical cord knot. Results: Three dimensional color Doppler ultrasound can diagnose the cord knot and eliminate the false knot. Conclusion: three-dimensional color doppler will be provides an objective and accurate diagnosis of true umbilical cord knot for clinic.