With the precision of equipment products and the complexity of the business environment, volume flexibility is becoming a vital derivation for equipment manufacturing enterprises to address manufacturing stability and competitive conundrums. To clarify the relationship among the manufacturing structure, manufacturing stability and volume flexibility, and answer the question of "How to choose the optimal flexible volume strategy for equipment manufacturing enterprises under series manufacturing structure", based on the series structure characteristic of the manufacturing system of equipment manufacturing enterprises, this paper conducts theoretical modelling and analysis. The results show that: Compared with the single link manufacturing structure, the optimal volume flexibility of the serial manufacturing structure is higher but the total manufacturing profit is lower; Under the serial manufacturing structure, equipment manufacturing enterprise is motivated to adopt a flexible manufacturing strategy; As the manufacturing stability of the pre-order manufacturing process 1 increases, the optimal manufacturing flexibility shows an inverted U-shaped trend; As the marginal cost of manufacturing flexibility increases, the optimal manufacturing flexibility and total manufacturing profit decrease. The above conclusions can provide useful decision-making references for formulating and implementing flexible manufacturing strategies for equipment manufacturing enterprises.