Objective Two dimensional gray scale blood flow imaging（B⁃Flow）was used to develop the left renal vein（LRV）and its surrounding vessels in children to evaluate the compression of LRV and to explore the application value of this technique in LRV. Methods A total of 18 children with nutcracker syndrome（NCS） diagnosed by CT in Children′s Hospital of Nanjing Medical University due to hematuria and proteinuria were enrolled as disease group and 17 children without related clinical symptoms and excluded NCS by CT examination due to non⁃urinary system conditions were enrolled as control group. The angle（θ）between the superior mesenteric artery （SMA）and the abdominal aorta（AO），the inner diameter of the dilated segment（a segment）before compression （Φa）and the inner diameter of the compressed segment（b segment）of the LRV（Φb）were measured by B⁃flow. Peak velocity（Va）of a segment and peak velocity（Vb）of b segment were measured by pulsed Doppler. The ratios Ⅰ=Φa/Φb and Ⅱ=Vb/Va were calculated.Two independent sample t test was used to compare the differences between the two groups. The ROC curve was drawn to obtain the best cut⁃off value，area under the curve（AUC）， sensitivity and specificity of each index alone and in combination in the diagnosis of NCS，and the diagnostic efficacy of each index was compared. P < 0.05 was considered statistically significant. Results The mean θ angle of the disease group（26.79 ± 9.06）° was significantly smaller than that of the control group（52.23 ± 12.77）°. The compression of segment b and the expansion of segment a in the disease group were generally more severe than those in the control group. The ratio Ⅰ（4.82 ± 1.14）was significantly higher than that in the control group（2.60 ±0.52）. The blood flow velocity of the compressed b segment in the disease group was significantly increased，and its ratio Ⅱ（8.98 ± 4.22）was significantly higher than that of the control group（3.73 ± 1.30）. The t test results of θ， Ⅰ and Ⅱ between the two groups all showed P < 0.001，and the difference was statistically significant. ROC curve showed that the AUC of θ，Ⅰ，Ⅱ alone and in combination for the diagnosis of NCS was greater than 0.95，and the combined diagnostic efficiency was greater than that of single index diagnosis，but the P values of the differences between the diagnostic methods were > 0.05，without statistical significance. Conclusion B⁃Flow proved to be a valuable diagnostic tool for NCS and could be used as a new ultrasound imaging for LRV in children.