Herein, we developed a novel composite chlorinated poly (vinyl chloride) (CPVC) loose nanofiltration (LNF) membrane, that allows molecules with molecular weights less than 200 Da to pass through while blocking those with molecular weights between 800 and 1000 Da. To fabricate this CPVC membrane, glucose (GL) was added to the co-deposition aqueous phase system dopamine (DA) and polyethyleneimine (PEI), followed by interfacial polymerization (IP) with trimesoyl chloride (TMC). The crosslinking of GL with TMC produced more polyester (PET), loosening the microstructure of the selective layer of the resultant membrane. The effects of GL/DA and GL/PEI on the microstructure was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Fourier transform infrared spectrometry (FTIR) and filtration performance (pure water flux (PWF), PEG800 rejection rate) of composite CPVC LNF membranes was investigated. Furthermore, this novel composite membrane was employed in the treatment of simulating reactive black 5 (RB5) dye wastewater, and the dye wastewater flux, RB5 rejection and the NaCl rejection rates were investigated. The effects of GL/DA and GL/PEI on the simulating RB5 dye wastewater treatment were also examined. The results stated that the GL/PEI had insignificant effect on the performance of the composite membranes. The increase of GL/PEI slightly augmented the PWF and RB5 dye wastewater flux. Intriguingly, the increase in the GL/DA significantly improved the PWF and RB5 dye wastewater flux and slightly decreased the rejection of PEG800, RB5 and the salt, demonstrating the loosening in the structure of the selective layer. The optimal GL/DA was 6/4, where the PWF 6.61 L/(m²·h·bar) and RB5 dye wastewater flux 5.23 L/(m²·h·bar) increased by 48.21% and 40.60%, respectively, compared to those at zero addition of the GL. The RB5 rejection rate was 93.68% and the salt rejection was 1.90%, which meant this novel composite CPVC LNF membrane can separate RB5 dye/salt perfectly.