The combined analysis of the discrimination performance of the atmospheric and oceanic high-spectral-resolution lidar (HSRL) can help the joint atmospheric and oceanic observation research. An atmospheric and oceanic HSRL system based on the field-widened Michelson interferometer (FWMI) discriminator is proposed in this work, which can be used to retrieve the 180-degree volume scattering function of oceanic and atmospheric particles. The core of the system is the combined-molecular dual channel, in which the molecular channel uses FWMI discriminator to filter the particle signal but transmit the molecular signal. It is shown that the retrieval error will increase proportionally with the particulate scattering ratio (the ratio of the total 180-degree volume scattering function to that of molecular), while the enhancing of the spectral discrimination ratio (the ratio of the molecular transmittance to the particulate transmittance) can significantly suppress the growth trend of the retrieval error. Because molecular scattering and particulate scattering are separated in the spectrum of oceanic HSRL, FWMI has a better discriminating characteristics in the oceanic HSRL than in the atmospheric HSRL. The proposed HSRL system based on FWMI can work in water and atmosphere, which is of great significance to the performance improvement of atmospheric and oceanic lidar.