The invention provides propargyl modified benzoxazine resin and a preparation method thereof. The molecular structural formula is as shown in the description. Tests show that the carbon residue rate of the prepared resin reaches 50.5%-64.8% at 800 DEG C. In the curing process of the benzoxazine resin, propargyl can be further subjected to crosslinking reaction with ring-opening crosslinking of anoxazine ring, so that the resin material forms a more compact covalent bond network system, and the benzoxazine resin has excellent thermal stability. The preparation process of the resin is relatively simple to operate and does not need complicated conditions, thereby being suitable for large-scale application.