A novel substrate integrated waveguide (SIW) slot antenna with high power-handling capacity in X band is proposed. The whole slot array antennas are designed on a single substrate, which takes the advantage of small size, low cost, and easy integration. The design process and simulated results of the slot array antennas are presented. The simulated results demonstrate that the presented novel SIW slot antenna has a power-handling capacity of 22.9 MW under vacuum condition, much higher than the conventional SIW slot antenna.