Abstract Knowledge of the morphology of nova ejecta is essential for fully understanding the physical processes involved in nova eruptions. We studied the 3D morphology of the expanding ejecta of the extremely slow nova V1280 Sco with a unique light curve. Synthetic line profile spectra were compared to the observed [O iii] λλ4959, 5007 and [N ii] λ5755 emission line profiles in order to find the best-fit morphology, inclination angle, and maximum expansion velocity of the ejected shell. We derive the best-fitting expansion velocity, inclination, and squeeze as V exp = 2100 − 100 + 100 km s⁻¹, i = 80 − 3 + 1 deg, and squ = 1.0 − 0.1 + 0.0 using [O iii] line profiles, and V exp = 1600 − 100 + 100 km s⁻¹, i = 81 − 4 + 2 deg, and squ = 1.0 − 0.1 + 0.0 using the [N ii] λ5755 line profile. A high inclination angle is consistent with the observational results showing multiple absorption lines originating from clumpy gases, which are produced in dense and slow equatorially focused outflows. Based on additional observational features such as optical flares near the maximum light and dust formation on V1280 Sco, a model of internal shock interaction between slow ejecta and fast wind proposed for the γ-ray emission detected in other novae seems to be applicable to this extremely slow and peculiar nova. Increasing the sample size of novae whose morphology is studied will be helpful in addressing long-standing mysteries in novae such as the dominant energy source to power the optical light at the maximum, optical flares near the maximum, clumpiness of the ejecta, and dust formation.