A method for determining the coefficient of thermal expansion (CTE) of concrete with optical lever system is introduced. In order to improve the system of traditional optical lever, vernier caliper was used instead of the scale plate to deduce the precise formula according to theories. The experiment was carried out to test the CTE of concrete with different aggregates. The results show that: when aggregate content was equivalent, the CTE of concrete increased with that of aggregate. Type of aggregate affected the CTE significantly.