Abstract: Monofilameut contact angle meter has been used to measure the critical surface tension of glass fiber treated by different cooupling agents.Because the critical surface tension of solid is a plysico-chemical parameter denoter the surface property of solid and it is only dependent on the nature of cover bet indepemlent of the internal constitution of glass filer.It is found that glass fibers trested lay different coupling agents have different surfere tensions, the order is as follows: 7114>KH550>A151 The components of coupling agent sedimeuted on surface of class fiber hive different effects on wetting property.