Abstract: The adoption of inert matrix fuel (IMF) can effectively reduce the amount of minor actinide (MA) in spent fuel of LWR from the source. In order to study the burnup characteristics of IMF, the two typical IMF schemes of PuO₂+ZrO₂+MgO and PuO₂+ThO₂ were selected, and the IMF reactivity with different amounts of PuO₂ was calculated. And the comparison among IMF, UO₂ and MOX was made. The results show that after 36 months operating, with the PuO₂ volume fractions of two types of IMFs from 2% to 10%, their k_inf values at the end of cycle are all above 1. But the burnup reactivity of PuO₂+ZrO₂+MgO scheme is greater than that of PuO₂+ThO₂. The amount of MA at the end of cycle in PuO₂+ThO₂ scheme is obviously smaller than the former. Under the same effective heavy metal weight percentage, the amounts of MA in MOX and UO₂ fuels at the end of cycle are both greater than those of the two types of IMFs.