Because MoSe₂ has broadband saturable absorption, and higher nonlinear refractive index. Compared with MoS₂, thin-layered MoSe₂ possesses very attractive properties, including narrow bandgap, low optical absorption coefficient, and large spin-splitting energy at the top of the valence band. The narrow bandgap and low optical absorption coefficient could make MoSe₂ more applicable than MoS₂. And the tunable excitation photoelectric effecthas great potential applications in the fields of photoluminescence, phototransistor, solar cells, nonlinear optics and other aspects. However, pure MoSe₂ has high photogenerated recombination rate, thus limiting its applications in some optical fields. By designing nanocomposites of MoSe₂, the photogenerated recombination rate of these materials can be reduced and their application field can be broadened. In this work, MoSe₂ nanocomposites are prepared by simple methods. The two-dimensional layered MoSe₂ nanosheets are combined with nanorods. By integrating the surface effect, small size effect and interfacial effect of CNT, the optical nonlinearity and optical limiting performance of MoSe₂ composites are improved. The CNT/MoSe₂ composite nanomaterials are first synthesized based on narrower band gap and lower light absorption coefficient of MoS₂ than those of MoSe₂ by growing MoSe₂ nanoparticles on the surface of CNT through a solvothermal method, and then is dispersed in methyl methacrylate (MMA) to prepare an organic glass by a casting method, and the MMA is polymerized into poly (methyl methacrylate) (PMMA). The nonlinear absorption (NLA), nonlinear scattering (NLS) and optical limiting (OL) properties of the CNT/MoSe₂/PMMA organic glass are studied by the modified Z-scan technique for the first time. The CNT/MoSe₂/PMMA organic glass exhibits the saturable absorption (SA) and a changeover from SA to reverse saturable absorption by adjusting input energy. The experimental results show that the CNT/MoSe₂/PMMA plexiglass exhibits better anti-saturation absorption and higher optical limiting properties than MoSe₂/PMMA and CNT/PMMA plexiglass. Besides, the NLA and OL properties of the CNT/MoSe₂/PMMA organic glass are enhanced compared with CNT/PMMA and MoSe₂/PMMA organic glasses, which can be attributed to the existence of the C=C double bonds in CNTs, the layered structure of MoSe₂ nanosheets, and the interfacial charge transfer between CNTs and MoSe₂. And the results demonstrate that the CNT/MoSe₂/PMMA organic glass is very promising for optical devices such as optical limiters and mode-locked/Q-switched lasers.