Abstract: In the ex-vessel steam explosion calculation, the corium jet fragmentation model affects the premixing parameters and phenomena such as generation rate and size of corium drops, the distribution of corium drops, corium drop solidification, void fraction and so on, and then has influence on the strength of steam explosion. Different corium jet fragmentation models (CONST model and KHF model) were used to calculate the ex-vessel steam explosion for advanced PWR based on MC3D V3.8 code in order to discuss the effect of corium jet fragmentation model on ex-vessel steam explosion calculation. It is shown that these two models give similar premixing conditions. At the time of melt bottom contact, explosion criteria of these two models are almost the same, so the strength of explosion triggering has a little difference, which indicates that these two models have a little influence on steam explosion calculation if the time of corium bottom contact is chosen as triggering time for advanced PWR. On the defined condition for advanced PWR, the maximum pressure near cavity wall is 20 MPa in approximation and the maximum impulse on cavity wall is smaller than 0.2 MPa•s.