How many users can a quantum cryptography network support when certain services are demanded? The answer to this question depends on three factors:the speed of quantum key distribution,the organization and traffic engineering of the quantum cryptography network,and the engineering of services.In this article we focus on the second factor which is lacked in the literature to our knowledge but in urgent need for constructing an optimized large-scale quantum cryptography network.In order to provide an overall understanding about a quantum cryptography network,we also briefly introduce the characteristics of quantum cryptography and service engineering. How many users can a quantum cryptography network support when certain services are demanded? The answer to this question depends on three factors: the speed of quantum key distribution, the organization and traffic engineering of the quantum cryptography network, and the engineering of services. this article we focus on the second factor which is lacked in the literature to our knowledge but in urgent need for constructing an optimized large-scale quantum cryptography network.In order to provide an overall understanding about a quantum cryptography network, we also briefly introduce the characteristics of quantum cryptography and service engineering.