Abstract: Bactericides used in hydroxyl propyl guar gum (HPGG) fracturing fluids are inclined to become decayed quickly, hence hindered well fracturing. In laboratory studies the conditions under which the bactericides were evaluated and the field conditions compared.Three factors were found affecting the decaying process of the bactericides.First, the bacteria used in standard evaluation process do not take into account those from fluid tanks. Second, the pH values of the bactericides used in HPGG (produced through alkaline crosslinking) fracturing fluids should not be less than 7. Consideration should be given to the changes in pH values by greater than 0.1 which will cause changes in the viscosity of the guar gum liquid, and the effectiveness of bactericides should be superior to that of pH value crosslinking modifiers used in HPGG fracturing fluids. Third, percent viscosity retention should be determined on the basis of the viscosities of HPGG of different concentrations and sand carrying capacity through crosslinking performance.