It is crucial for highly security-critical information systems to accurately control the disaster recovery activities. Using optimization theory, we present a disaster recovery planning mathematical model. The model uses mathematical method to express diverse entities in information and disaster recovery system such as applications, facilities, resources, sub disaster recovery plans, budget, etc. It classifies various resources according to their utilization and payment, and identifies the significance of applications and the conflicts among sub disaster recovery plans. Through expressing relationships among applications, facilities, resources and sub plans, this model selects the best set of sub plans. This model has less subjective parameter and can evaluate disaster recovery planning objectively and quantitatively.