Currently existing extensometer may not completely correspond with the requirement of precision and linearity in the measurement of enormous structure's strain. The objective of this research is to describe a new structure of high precision extensometer sensor. An half of an annular chip serves as the elastic element of the new extensometer. Theoretical analyses and discussions about the accuracy and linearity of this new elastic element are conducted. Based on the oil sucking machine, the new structure of high precision extensometer sensor is installed to measure the micro strain as an experiment. Statics calculation examine that the deflection of measuring terminal shows linear relationship with the strain of the elastic element in certain position. Theoretically, the feasibility of a series of elastic elements is discussed. The results can provide reference value and significance in the innovation and design of industrial measurement.