A power transmission system of a vehicle may include a CVT device having primary and secondary pulleys, a planetary gear set having first, second, and third elements, a first shaft connected to an engine and fixed to primary pulley, a second shaft fixed to secondary pulley, a third shaft fixed to first element, a fourth shaft fixed to second element and selectively connectable to first shaft and a transmission housing, a fifth shaft fixed to third element, a sixth shaft externally gear-meshed with second shaft, and a seventh shaft externally gear-meshed with third shaft and selectively connectable to sixth shaft, wherein first shaft is coaxially superposed with third, fourth, and fifth shafts, second, sixth, and seventh shafts are disposed in parallel with planetary gear set, and second, fifth, and sixth shafts, third and seventh shafts, and seventh shaft and a differential communicate torque through first, second, and third gear sets.