Quality and energy efficiency are two critical concerns associated with the production of biomass pellets. This study elaborates methods to improve the quality of biomass pellets by using a new additive solution (carboxymethyl cellulose (CMC)) and its influence on pellet physical and mechanical properties during the densification of three types of agricultural waste (cotton stalks, wheat straw, and rape straw). Simultaneously, the cohesion and binding mechanisms were analyzed with attenuated total reflectance infrared spectra (ATR-FTIR) and light microscopy (LM). The results show that adding CMC lowers the energy consumption and increases the pellet quality by improving relaxed density, compressive strength, and durability for cotton stalks and wheat straw. However, adding CMC to rape straw decreased the pellet quality. Our results showed that addition of CMC leads to electrostatic forces among the particles that might be responsible for the cohesion strength of biomass pellets, which may be attributed to the formation of polyelectrolytes. The electric dipole from water molecule in biomass and OH groups on the CMC formed the hydrogen bond. In addition, strong bonds, similar to solid bridges, were formed at the interfaces between CMC and biomass solid particles. These interactions enhance interparticle bonding in the pellets, thereby improving the product quality and providing an efficient means to convert agricultural waste into biomass energy.