1. The starting dose should be small. It is advocated to start with a small dose, starting with L-T4 of 25-50mg/time, or even 12.5mg to start with (10-20mg/time for dry thyroid tablets), and then gradually increase the dose, once every 2-4 weeks, with each increment of L-T425-50mg/time, and the maintenance dose can be reached in 2-3 months until TSH and T4 return to normal. For some patients who have difficulty in increasing the dose, digitalis or psoralen can be added while taking thyroid hormone preparations. 2.The half-life of thyroxine is long, and the plasma drug concentration is relatively stable after taking the drug, so it can be taken once a day. 3.According to our clinical observation on 38 cases of primary hypothyroidism patients treatment, the equivalence between three thyroid hormone preparations is: L-T4100mg≈ dry thyroid tablets 40-60mg≈ T330-40mg. 4.The determination of hypersensitive TSH can avoid replacement dose overdose, the equilibrium of TSH takes longer time, and the TSH reaches equilibrium only 4-6 weeks after changing the dose of L-T4.