Mild hydronephrosis of the left kidney can be examined by CT, but ultrasound is the preferred test for hydronephrosis. Compared with CT, ultrasound examination of hydronephrosis is more convenient, clear, intuitive and less expensive. Mild hydronephrosis in the left kidney can be seen directly on the ultrasound image. The image will show a mild separation of the pelvis and calyces of the left kidney. After finding hydronephrosis, the sonographer will also look for dilatation of the upper and middle portions of the left ureter, as well as for the presence of stones on the left side of the kidney and in the upper and middle portions of the left ureter, where they can be clearly visualized. Urological diseases, such as kidney, bladder, etc., can be preferred to ultrasound examination, in the case of ultrasound can not be clear lesions, can consider the addition of CT examination. Patients with mild hydronephrosis of the left kidney are advised to go to regular hospitals to have the test results prescribed and evaluated by specialized doctors.