We performed a joint measurement of terahertz waves and the second harmonic interference generated by ionizing atomic argon gas in a thin jet placed in the Releigh range of a focused phase-locked two-color laser field.The measurements shown that the optimal phases for terahertz radiation changealong the focal length depended on the gouy phase shift.This finding implies that terahertz radiation can be used to measure the relative phase of the two-color field, even the carrier-envelope phase in situ.