We studied the nematic liquid crystal (NLC) aligning capabilities using the new alignment material of a-C:H thin film as working gas at 30W rf bias condition. A high pretilt angle of about 5$^{circ}$ by ion beam(IB) exposure on the a-C:H thin film surface was measured. A good LC alignment by the IB alignment method on the a-C:H thin film surface was observed at annealing temperature of 250$^{circ}C$, and the alignment defect of the NLC was observed above annealing temperature of 300$^{circ}C$. Consequently, the high LC pretilt angle and the good thermal stability of LC alignment by the IB alignment method on the a-C:H thin film surface as working gas at 30W rf bias condition can be achieved.