In order to know the main controlling factors of mechanical degradation of partially hydrolyzed polyacrylamide （HPAM）in pore-throat model，the mechanical degradation experiments of partially hydrolyzed polyacrylamide（HPAM）for polymer flooding in the pore-throat model were carried out，and the effect of flow rate，concentration，pore-throat ratio and other factors on the mechanical degradation was studied. The experimental results show that the main factors of mechanical degradation of HPAM in the pore-throat model are flow rate and pore-throat ratio，and the concentration and total salinity of formation water have little influence on the mechanical degradation of HPAM. The apparent viscosity loss caused by the mechanical degradation of HPAM in the pore throat increases with the flow rate，and there is a“critical flow rate”that the polymer molecules begin to degrade rapidly，and a“limit flow rate”at which the degradation reaches the limit. When the HPAM passes through the tandem pore-throat model，the mechanical degradation occurs mainly in the first four porethroat models，which indicates that the key position of the mechanical degradation of HPAM in the reservoirs is the near bolehole zone.