Abstract: According to the experience of practical start-up, analysis and calculation of reactivity accession procedure were carried out for start-up on the reactor by transient analysis code RETRAN-02. Then a reasonable reactivity accession procedure was put forward. The latency time could be shortened and the rod-lift times could be reduced by increasing reactivity increment. It can ensure the security of passive start-up and improve working efficiency. The working intensity of operator was greatly lightened and the start-up time was obviously shortened. It can provide basilica reference for the establishment of reactivity accession procedure for start-up on reactor and the execution of secure start-up.