The causes and control methods of the magnetic parameter drifts for magnetic bubble LPB garnet films are investigated. It is considered that the main cause of the magnetic parameter drifts is the garnet heterogeneous nucleation and growth of the supersaturated melt. The phenomenon of melt compositional drift is explained in terms of the effective concentration of melt nutrient Reff = R4-Rn-Re, where R4 is the original concentration of the nutrient, Rn is the nutrient concentration consumed by the heterogeneous nucleation and growth, and Re is the nutrient concentration consumed by the LPE films. The eonsumption of melt nutrient concontration in LPE process is equal to Rn+Re, and the effect of Rn on the magnetic parameters of LPE garnet films is much greater than Re. In the reheating control process Rn= 0, and the melt is relatively stable. Stirring of substrates may accelerate the heterogeneous nucleation and growth of the melt.