The relationships between tensile stress and strain of concrete with incorporated 0%, 5%, 10%, 15% metakaolin (MK) were studied. Test results show that, with the raising of MK replacement, the tensile strength and peak strain of concrete increase and the compressive strength of concrete increases significantly, but the tensile elastic modulus is nearly same and the ratio of tensile strength to compressive strength is decreased. With the raising of MK replacement, the area covered by descending curve of over peak stress is improved when 5% and 10% of cement replaced by MK. When content of MK is lower, such as 5%, the workability of concrete is all the same as that without MK. When the content of MK is 15%, the slump of concrete is decreased about 20%. But the slump could be kept the same with that without MK only by adding another 20% superplasticizer. Therefore, the MK is a very efficient enhancing addition for high performance concrete.