For the core problem of ground safety control—the relative criticality estimation of ground protected objects in the rocket launch process, the relative criticality algorithm of ground protected objects is proposed in the paper. This algorithm transforms the measurement of the relative criticality for ground protected objects into cost function which considers the rocket’s current fall point，the distribution of rocket’s wreckage and poison gas, the population and the important establishments of the objects, realize the comprehensive evaluation of the relative criticality for different objects. To verify the effectiveness of this algorithm, it is applied to a decision support system to achieve the quantitative evaluation of the ground protected objects in several rocket launching tasks. This algorithm provides quantificational judgment evidence for rocket safety control officers in effective decision- making for safety control of the rocket launching.