Objective Measure the epicondyles of the distal femur on magnetic resonance image(MRI), in order to locate presicely the surgical transepicondylar axis(STEA) in total knee arthroplasty(TKA) and to provide theoretical basis for the designing of the size of the femoral component. Methods Totally 78 normal knees of Chinese individuals were studied. The images of coronal, sagittal and traverse sections of the knee were obtained by magnetic resonance image. Measurement included the width of the STEA, distance between the epicondyles and the joint line, anterior posterior width of the medial and lateral epicondyles, posterior condyle angle. Results The width of the STEA averaged(79.55±4.90)mm in males, and femles(71.18±4.22)mm. The distance from the epicondyles to the joint line was correlated with the width of the STEA, so was the anterior posterior width of epicondyles. PCA averaged(4.22±2.07)°. Conclusion The size of the epicondyles in Chinese is significantly smaller than that of the Westerns. The ratio between anterior posterior width of the medial epicondyle and the width of the STEA is 0.84, and is 0.87 between anterior posterior width of the lateral epicondyle and the width of the STEA. The distance from the epicondyles to the joint line is helpful to locate the STEA. The reliability is poor to lo