Preparation of carbon nanotube (CNT) films with both high strength and high elongation is a key challenge to wide application of CNT. A simple method has been investigated to design and prepare high strength and elongation CNT films. This was achieved using a thiol-ene click reaction between the double bond groups of the CNT films and the thiol groups of mercaptans. The effects of mercaptans contents in the functionalized CNT film, click reaction time and the ratio between mercaptans and CNT film on their mechanical strength have been researched. The tensile strength of the functionalized CNT film was 560% higher than that of the prime CNT film. The improvement and functionalized mechanism of CNT film were studied by scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and Fourier transform infrared spectroscopy. Compared with prime carbon nanotube films, the inter-tube interaction of the functionalized CNT films has been changed from weaker van der Waals force to stronger chemical bond, and the cross-link network of mercaptans chain connected CNTs also enhances the load transfer among the CNTs and reduces the distance of the interfacial slippage, which contributes to the improved mechanical properties. This method about improving strength of CNT films will supply a new strategy for preparing high strength CNT film.