We have studied systematically the effects of temperature, time, and pressure on the process of hydrogen absorption in LaFe11.5Si1.5 compound. Results show that hydrogen absorption can increase the lattice parameter of the compound without changing its crystal structure. The LaFe11.5Si1.5H1.6 compound can be prepared at a hydrogen pressure of 0.0987 MPa at 423 K with uniform distribution of hydrogen. Hydrogen absorption can also increase the Curie temperature obviously, decrease the thermal hysteresis and maintain the magnetic entropy change at a high standard. With prolonged exposure time in air, the variation of the Curie temperature and magnetic entropy change of LaFe11.5Si1.5H1.6 compound are very small, implying that the magnetic thermal performance of hydride alloy has a good time stability.