Carbon nanotubes (CNTs) have a strong tendency to entangle and aggregate each other, which is the key problem for them to achieve excellent performance in conductive composites. Therefore, the objective of this study is to modulate the aspect ratios and -COOH content of cellulose nanocrystals (CNCs) and use CNCs with different aspect ratios and -COOH content as a new type dispersant to enhance the dispersibility of CNTs in aqueous phase as well as the properties of CNTs-CNCs composite nano-membranes (CNMs). It was found that the addition of CNCs as well as their reduction in aspect ratio and the increase in -COOH content, significantly improved the CNTs dispersion as well as the mechanical and electrical properties of CNMs. Among them, the dispersibility of CNTs, the tensile and sensing performance of CNMs were more affected by the aspect ratio of CNCs. The highest tensile strength, toughness and resistance change rate of the CNMs were 73.2 MPa, 2.5 J/m3, and 33.3%, respectively. On the other hand, the conductivity of CNMs was jointly affected by the aspect ratio and -COOH content of CNCs, but the influence of -COOH content was more direct. When the aspect ratio of CNCs was below 50 and the -COOH content was above 0.65 mmol/g, the conductivity of CNMs reached over 20 S/cm.