Three kinds of phenolic resins have been synthesized at pH of 3 (with phenol/formaldehyde molar ratio of 1∶0 75 catalyzed by oxalic acid), 8(with phenol/formaldehyde molar ratio of 1∶1 4~1∶2 4 catalyzed by KOH) and 14(with phenol/formaldehyde molar ratio of 1∶1 2~1∶1 5 catalyzed by KOH), respectively. Investigation on the crosslinking reaction between phenolic resins and borate showed that resin synthesized at basic condition can chelated with borate quickly by passing CO 2 through the resin sand. The results indicated that the cured casting of the resin synthesized at pH=14 possessed the highest mechanical strength.