Elastic modulus of concrete at early age can not be tested by standard test methods. In order to solve this problem, thermal stress test was suggested. Based on temperature stress testing machine, elastic modulus of concrete at early age can be accurately examined by selecting high precision load cell（accuracy 01kN） and controlling displacement increment in the range of 10～15μm in a very short time, i.e. 5 seconds. Using equivalent age as time scale, combined elastic modulus data tested from tz，1（age at which first zero stress has been reached） to 48h by thermal stress test and the data tested from 3 days to 28 days by standard test method, the function of elastic modulus development has been created.