The effects of lattice vibration on the system in which the electron is weakly coupled with bulk longitudinal optical phonons and strongly coupled with interfac e optical phonons in an infinite quantum well were studied by using Tokuda' line ar-combination operator and a modified LLP variational method. The expressions for the effective mass of the polaron in a quantum well QW as functions of the we ll's width and temperature were derived. In particular, the law of the change of the vibration frequency of the polaron changing with well's width and temperatu re are obtained. Numerical results of the effective mass and the vibration frequ ency of the polaron for KI/AgCl/KI QW show that the vibration frequency and the effective mass of the polaron decrease with increasing well's width and temperat ure, but the contribution of the interaction between the electron and the differ ent branches of phonons to the effective mass and the vibration frequency and th e change of their variation with the well's width and temperature are greatly di fferent.