The radiation detectors based on the third era semiconductor material silicon carbide (SiC) with wide energy band gap are the most promising ionizing radiation detectors in high temperature and harsh radiation environment. This paper illustrated several important advantages of the SiC neutron detector and described its fabrication and detection principle briefly. Furthermore, we evaluated the neutron sensor’s measurement performance when detecting the 2.5MeV and 14MeV neutrons under different conditions of sensor’s active layer thickness and polyethylene converter film thickness based on MCNP simulation. According to the results of simulation, the sensor’s optimal configuration was designed. For the sensor whose radius and depletion layer thickness are 3mm and 30μm respectively, the detection efficiency can reach 3.16×10-18 coulomb per neutron (c/n) and 1.80×10-17 c/n for 2.5MeV and 14MeV neutrons respectively. When adding a polyethylene converter film of 90μm thickness to the above sensor, the detection efficiency to 2.5MeV neutron will be 3.7 times that without neutron converter film; and with the converter film of 2mm thickness, the detection efficiency to 14MeV neutron will be improved by 246%.