Abstract: Transient performance of CSR1000 core during the control rod (CR) dropping into the core was analyzed and evaluated using the 3D SCWR transient analysis method. The 3D CR drop transient analysis shows that while the high worth CR drops into the core, the core power descent rate exceeds the shut-down setting value, then the protection shut-down will be triggered. While the low worth CR drops into the core, the core power descent rate isn’t quick enough to exceed the shut-down setting value, and the protection shut-down won’t be triggered. The maximum cladding surface temperature (MCST) retains lower than safety criteria 850 ℃ in the transient process no matter the dropped CR worth is high or low. The safety of CSR1000 core can be guaranteed during the CR dropping into the core under the significant water density reactivity feedback and the essential reactor protection shut-down measures.