An earphone structure with no-section-difference design is provided, including an earphone casing, a transmission wire and a strain relief thereof. The earphone casing has a joining end to join with a joining section of the transmission wire The strain relief is formed at where the earphone casing and the transmission wire are joined. Along from the earphone casing to the transmission wire, diameter of the strain relief decreases progressively to a same diameter with that of the transmission wire, thereby providing a no-section-difference exterior look thereof between the strain relief and the transmission wire.