The invention provides a low-profile radial-line helical antenna comprising a coaxial line, a first metal layer, a first dielectric substrate, a second metal layer, a second dielectric substrate, and a third metal layer. The layers are laminated successively. A first helical line is formed at the first metal layer; a second helical line that is opposite to the first helical line and is coupled with the first helical line is formed at the second metal layer; the third metal layer is grounded; and the coaxial line passes through the first metal layer, the first dielectric substrate, the second metal layer, the second dielectric substrate, and the third metal layer successively. An outer conductor of the coaxial line is connected with the third metal layer electrically; and an inner conductor of the coaxial line is connected with an initial point of the first helical line electrically. According to the invention, on the basis of coupling between the second helical line and the first helical line, a phase requirement on the reflection path of the first helical line can be reduced and thus the distance requirement between the first helical line and the third metal layer can be reduced; the antenna size is reduced; and the low-profile radial-line helical antenna is realized.