The tearing mechanisms of woven fabrics are analyzed,conclusion can be drawn that the tearing strength is relatively steady and the size of the del won't alter significantly under single rip method while the tearing strength will increase gradually till go up to maximum as well as the size of the del will be bigger and bigger under trapezoid tearing method as the yarns brake one by one.Tearing strength tests of four fabrics have been done by using those two methods,the tearing curves show good agreement with the tearing mechanism we have deduced.At the same time we discuss the importance of 2D woven fabrics' mechanical properties to 2D textile composites.