The heterojunction of single-wall carbon nanotubes (SWCNTs) and perovskite quantum dots (QDs) shows excellent photodetection performances due to the combination of the advantages of high carrier mobility of SWCNTs and high absorption coefficient of perovskite QDs. However, the band structure of a SWCNT is determined by its atomic arrangement structure. How the structure of SWCNTs affects the photoelectric performance of the composite film remains elusive. Here, we systematically explored the diameter effect of SWCNTs with different bandgaps on the photodetection performances of SWCNTs/perovskite QDs heterojunction films by integrating semiconducting SWCNTs (s-SWCNTs) with different diameters with CsPbBr₃ QDs. The results show that with an increase in diameter of s-SWCNTs, the heterojunction exhibits increasing responsivity (R), detectivity (D*), and faster response time. The great improvement in the optoelectronic performances of devices should be attributed to the higher carrier mobility of larger-diameter SWCNT films and the increasing built-in electric field at the heterojunction interfaces between larger-diameter SWCNTs and CsPbBr₃ QDs, which enhances the separation of the photogenerated excitons and the transport of the resulted carriers in SWCNT films.