Nicotinamide, also known as vitamin PP, is component of coenzyme Ⅰ and Ⅱ, and it turns into a coenzyme for most of dehydrogenases. Pimelic acid has also been utilized previously as a cocrystal former. A cocrystal of nicotinamide and pimelic acid exists in two different polymorphic form-Ⅰ and form-Ⅱ. It is important to find a suitable technical means in the pharmaceutical field since the polymorphs have different physio-chemical properties which influence their solubility, stability and also other performance characteristics. The absorption spectra of nicotinamide-pimelic acid cocrystal were measured using terahertz time-domain spectroscopy ranging from 0.2 to 2.2 THz at room temperature, and the absorption peaks have obvious difference. Form-Ⅰ and form-Ⅱ have five characteristic absorption peaks at 1.51, 1.73, 1.94, 2.01, 2.17 THz and 1.66, 1.74, 1.88, 2.02, 2.16 THz, respectively. Form-Ⅰ has three strong absorption peaks at 1.94, 2.01 and 2.17 THz, while form-Ⅱ has two strong absorption peaks at 2.02 and 2.16 THz. Density functional theory was used to simulate the polymorphs of the nicotinamide and pimelic cocrystal. The calculated characteristic peaks were in accord with those in the experiments. The results showed characteristic absorption bands come from skeletal and hydrogen bond vibrations. This research suggested that terahertz time-domain spectroscopy technique is important for applications in solid-state analytical tools to distinguish polymorphs of cocrystal in pharmaceutical fields.