Aiming at the characteristic of water quality and the running situation of the chemical circulating cooling water system,the effect of the three factors (the concentration of pre-film agent,pH and time)on the pre-film result hasbeen investigated in lab.Then,the range of the three factorshasbeen confirmed.At the same time,the concentration of Ca₂₊ and the way to adjust pH when pre-film iscarrying on have been probed.Since the Cu₂₊ is high in the processof pre-filming,BTA is added to it in order to decrease the bad influence.At the end,reasonable and effective pre-film running plan isput forward.