In this paper, the molecular weight degradation phenomenon of polymers in GPC elutive process is investigated systematically using a low angle laser light scattering（LALLS）detector coupled to GPC with four different series of columns （Styragel, μ-Styragel, ultra-Styragel and Shodex-800）and using a wide range of molecular weight（2.3×10,3,～1×10,7,）of narrow MWD polystyrene samples in THF over a wide range of flow rate（0.4～2.6ml/min）. Results show that molecular weight degradation phenomenon in GPC elutire process with all the series of columns are serious at any flow rate when the molecular weight of polystyrene sample is equal to or more than 10,7,. For the four series of columns, the limit of molecular weight below which the degradation phenomenon will not take place, is respectively: （1）Shodex-800 columns: 5.8×10,6, （2）Styragel columns. 3.8×10,8, （3）μ-Styragel columns: 2.7×10,8, （4）ultra-Styragel columns: 6.7×10,5,. Above the limit, the molecular weight degradation phenomenon will occur in varying degree. In such cases, the effect of flow rate is sensitive, molecular weight of polymer will decrease with the increase of flow rate.