The key to diagnose nut cracker phenomenon (NCP) is left renal vein (LRV) high pressure, LRV pressure difference is the most direct and objective diagnostic criterion, and it is internationally recognized that LRV pressure difference of 0.49KPa can diagnose NCP. At present, the clinical diagnosis of NCP mainly relies on ultrasound examination: the ratio of the internal diameter of the dilated end of the left renal vein to the end of the compressed stenosis is greater than 3 times, but this method cannot be quantified and cannot determine the severity of the disease and effective follow-up. In this project, the theoretical derivation of LRV pressure difference is based on the law of energy conservation and the Burr’s effort equation. Color Doppler has the advantage of detecting blood flow velocity, and the LRV pressure difference can be inferred indirectly by measuring the velocity of the compressed segment of the left renal vein V1 and the velocity of the dilated segment V2 (equation: ΔP = P2 – P1 = 1/ 8ρ(V12 – V22) + ρg (h1 – h2) = 132 (V12 – V22) + 10348.8 × Δh, the criterion for this method: ΔP >= 499 Pa for a confirmed case) and thus a definitive diagnosis of NCP. This method can not only accurately diagnose NCP, but also provide more information for the diagnosis of difficult cases, which can be useful for quantitative diagnosis, disease judgment and disease follow-up.