The elastic moduli of spring steels were measured by the ultrasonic pulse method and influencing factors on elastic moduli were discussed quantitatively. Results obtained are as follows : (1) Elastic moduli of spring steels depend on heat-to-heat variation, material specification and conditions of heat treatment. (2) A new parameter described by temperature and time of the tempering condition was proposed to explain the effect of tempering conditions on elastic moduli. (3) Diffusion process of carbon was pointed out as the reason of variation of elastic moduli due to the tempering treatment. (4) Linear models where independent variables are contents of C, Si, Ni, Cr and Cu in mass%, reciprocal of tempering temperature in K, and natural logarithm of tempering time in h, can be used to explain the moduli with an accuracy of 0.5%. (5) These models can't be applied for spring steels containing Vanadium.