We have studied the liquid crystal (LC) alignment, the pretilt angle generation, and the annealing behavior for a nematic liquid crystal (NLC) on the homogeneous polyimide (PI) surfaces by using the rubbing method and the ion beam (IB) method. An excellent LC alignment of the NLC on the PI surface with rubbing and IB irradiation were observed. The pretilt angle of NLC on the homogeneous PI surface for the rubbing method is decreased from $4.5^{circ}$ to $3.5^{circ}$ as rubbing time is increased, that of the for the IB irradiation method is decreased from $0.5^{circ}$ to $0.1^{circ}$ as the time of IB irradiation is increased. After the annealing, the pretilt angles of the rubbed PI surfaces increased up to $4^{circ}$, these of the IB irradiated PI surfaces little increased. It is considered the side chain of the rubbed PI show the its abilities of the original capacities, while the side chain of the IB irradiated PI cannot show the its abilities of the original capacities due to the IB has already destroyed the side chain of the PI.