An amniotic fluid index of 120mm is normal. In pregnancy, our B-mode ultrasound is a very important auxiliary test, not only to measure the amount of amniotic fluid, but also to understand the condition of the fetus and to rule out fetal abnormalities. there are standards for diagnosing amniotic fluid by ultrasound, in general, the maximum dark area of amniotic fluid, that is, the vertical depth of amniotic fluid is generally normal 3-7cm, or 30-70mm, while the amniotic fluid index is generally 80-180mm. Therefore, the amniotic fluid index of 120mm is normal. Amniotic fluid index >250mm is called excessive amniotic fluid, while amniotic fluid index <50mm is called too little amniotic fluid, too much amniotic fluid and too little amniotic fluid have certain effects on the fetus. During pregnancy we should pay attention not only to the fetal movement but also to the ultrasound amniotic fluid.