In order to provide different quantum key service, trusted relay quantum key distribution networks with quantum key pool was studied. Firstly, relationship between packet delay and quantum key pool was analyzed. The formula was given, which showed that the mean packet delay is related to the quantum key generation rate, the initial length of quantum key, the mean length, arrival time and arrival rate of packets. The theory and simulation results verified the accuracy of the delay analysis. Next, the key providing service was classified into three types: guaranteed, prioritized and besteffort key service. Correspondingly, prereserving, hopbyhop jumpingqueue and hopbyhop queuing approaches were presented to realize the above differentialized key services. Finally, simulation results verified the efficiency of the differentialized service providing scheme.