By statistically analyzing the information of PHM items which have been already accomplished in various countries, the original data of the technology readiness level and comparative schedule delay are gained. By the method of translation into linear regression, the regress functions of technology readiness level with average comparative schedule delay, and technology readiness level with maximal comparative schedule delay are established. On the assumption that the comparative schedule delay is obedient to normal distribution, the probability relationship of schedule risk with technology readiness level is established. Then, the relational graph of schedule risk and schedule allowance with technology readiness level is drawn. The research shows that when PHM technology readiness level achieves seventh grade, the schedule risk is within twenty percent, which is of an acceptable range.