In the presence of the initiator benzoyl peroxide (BPO), maleic anhydride (MAH) was grafted onto a kind of H-1 type fischer-tropsch wax by melt grafting process to improve the hardness and other indicators of Fischer-Tropsch wax. The experimental results show that, when the reaction lasted for 20 min at the reaction temperature of 140 ℃, the amount of maleic anhydride （MAH）was 5.0 g and the amount of initiator （BPO）was 4.0 g, the grafting rate reached 1.53% while the product's penetration degree was 1.6(0.1 mm). From the infrared spectroscopy (IR), we can see that MAH had been successfully grafted to the fischer-tropsch wax.