The heating power and charging oil quantity of the closed hydraulic system of the main drive of a shield are analyzed and calculated on basis of the working principle and oil charging mechanism of the closed hydraulic system. The calculation formula for the replacing oil quantity and the charging oil quantity of the closed hydraulic system are obtained and the oil replacing coefficient and oil charging coefficient are worked out. During the calculation, the oil running out of the closed hydraulic system is regarded as an integral part, so as to avoid discussion and calculation of the quantity of the leaked oil and the quantity of the replaced oil. The theory proves that the quantity of oil charged is sufficient. The paper can provide reference for the selection of oil charging pumps in the future.