Magnesium sulfate is mainly a drug that blocks the synthesis and release of uterine agonists, magnesium ions act directly on muscle cells to relax smooth muscle, thus inhibiting uterine contractions and preventing preterm labor. But in the use of magnesium sulfate should pay attention to its adverse reactions, renal insufficiency or blood magnesium accumulation may appear dizziness or dizziness, overdose can lead to electrolyte imbalance, secondary to cardiac arrhythmia, intravenous injection rate should not be too fast or too much dose. In the process of using drugs and medication, must do the following aspects of testing: 1, knee reflex must exist; 2, respiration per minute must not be less than 16 times; 3, urine volume of not less than 25mL per hour; 4, must have 10% of calcium gluconate 10mL , do the antidote to magnesium poisoning.