Abstract: The 2,2,6,6−Tetramethylpiperidine−1−oxyl radical (TEMPO) oxidation was used for preparation of cellulose nanofibers (CNF) with different carboxyl contents. Then the prepared CNF was used as the dispersing agent to disperse carbon nanotubes (CNTs) and the concentration of CNF−CNTs dispersion was measured by Lambert−Beer’s law to study the dispersion effect of CNF with different carboxyl contents. In addition, the CNF−CNTs/thermoplastic polyurethanes (TPU) composite film was prepared by pumping CNF−CNTs fillers in the prepared electrospun TPU film through vacuum filtration. The influence of carboxyl content of CNF on the strain sensitive performance of CNF−CNTs/TPU composite film was investigated. The result shows that, with the increase of the carboxyl content of CNF, the CNF has a better dispersion effect on CNTs, and the prepared CNF−CNTs/TPU composite film possesses a larger workable strain range. When the carboxyl content of CNF achieves 1.698 mmol/g, the CNF−CNTs/TPU composite film displays a large workable strain range of 507% and a high gauge factor of 335, exhibiting excellent strain sensitive performance.