We propose a novel gain-assist lossless hybrid plasmonic strip waveguide based on active semiconductor material as loss compensation.The proposed plasmonic waveguide is composed of strip semiconductor,dielectric mater ials and a silver membrane.The semiconductor strip is optically or electrically pumped as gain medium to provide gain to compensate the loss of the propagating optical signal in the proposed waveguide.The modal characteristics and guiding properties of the proposed waveguide are theoretically investigated using the finite elements method at the wavelength of 1550nm to target potential applications in telecommunications.The results show that this proposed waveguide can support a propagation length of 10μm under the subwavelength confinement. The corresponding normalized modal area and FOM are 0.011and 82, respectively.With the help of the gain medium made of active semiconductor material,the proposed waveguide supports the lossless propagation of the optical signal to realize unlimited propagation length under the subwavelength confinement.In addition,the sandwich-like structure of the proposed waveguide is very simple,which makes the proposed waveguide easy to be optically or electrically pumped and fabricated.The lossless hybrid plasmonic strip waveguide may have potential applications in optical interconnections,photonic integrated circuits,short-distance on-chip optical communications and optical information processing.