The blood amniotic fluid is common in the following three cases: 1. placenta abruptio, after placenta abruptio the blood after the placenta accumulates between the placenta and the uterine wall, the pressure increases, the blood penetrates into the myometrium, penetrates the plasma membrane layer and the amniotic layer, so the blood amniotic fluid appears. 2. placenta praevia, the placenta praevia appears repeated vaginal bleeding, especially when the bleeding amount is large combined with premature rupture of the fetal membranes, the blood amniotic fluid appears. 3. incomplete rupture of the uterus. It is common in long labor, obstructive obstructed labor, excessive contraction of the uterus, excessive elongation of the lower uterine muscles, formation of pathological constriction ring, partial rupture of the myometrium, blood penetration through the plasma membrane layer into the amniotic fluid, bloody amniotic fluid, bloody amniotic fluid found during pregnancy, all should be terminated in time.