The invention discloses a rotary switching dual-purpose washbasin faucet device which comprises an upper half fixed structure, a lower half rotary structure, upper and lower annular clamping grooves, upper and lower device fixing springs, a pipeline connection structure with convex and concave portions, a rotary fixing bearing, a front face water outlet and a back face lengthening water outlet. When the rotary switching dual-purpose washbasin faucet is in normal use, the front face water outlet is outward, the back face lengthening water outlet is inward, a lengthening device is tightly attached to a pipeline water outlet, use is not affected, and meanwhile the device is simple and attractive. When the rotary switching dual-purpose washbasin faucet needs to be lengthened for use, the rotary device is pulled downwards, rotated by 180 degrees and then released, and therefore the lengthening function can be achieved; and the requirement for lengthening the washbasin faucet is met conveniently and rapidly, and the rotary device can be switched to the front face for normal use after lengthning use is finished. The device is compact in structure, concise and visual in design, convenient and fast to use and easy to maintain.