The phenol formaldehyde （PF） resin samples under 16 different synthesis conditions were measured by gel penetration chromatographic instrument （GPC）. The resin quality index and molecular weight was gained. The results showed that if the mole ratio of phenol∶formaldehyde∶NaOH was 1∶2.1∶0.1, synthesis time went beyond 180 min , then the resin’s disperse index was smaller and the molecular was well distributed and the spectra peak was stability. The proportion of molecular distribution between 200～400 was 98.3%. Solid content was 49.8%. Free phenol content was 0.18%. Free formaldehyde content was 0.14%. Brominable substance content was 15.5%. Resin viscosity was 8.8 mPa·s . pH value of resin was 9.23.The ability of dissolve in water was beyond 7.5.