Cardiovascular Magnetic Resonance (CMR)-based T1 mapping and Heart Deformation Analysis (CMR-HDA) can assess the myocardial tissue characteristic and strain of cardiomyopathy. Whether they can assess cardiac abnormality of hypothyroidism (HT) is unknown. We aim to analysis left ventricular (LV) T1 values and strain of patients with overt HT (OHT) and subclinical HT (SHT) with CMR-based T1 mapping and HDA. This study prospectively included 32 OHT patients, 23 SHT patients and 27 healthy controls who underwent CMR. LV T1 mapping was obtained with a Modified Look-Locker Inversion Recovery sequence while LV circumferential strain (LVCS) and radial strain (LVRS), LV longitudinal strain (LVLS) were respectively analyzed on the short-axial and four-chamber cines with HDA. LV Eject Fraction among three groups were similar (p = 0.676). LV myocardial T1 correlated with LVCS (r = 0.734, p < 0.001) and LVRS (r = − 0.340, p = 0.011). LV myocardial T1 of OHT patients significantly increased in comparison with SHT patients (t = 5.403, p < 0.001) and normal controls (t = 10.197, p < 0.001), meanwhile, LV myocardial T1 of SHT patients were higher than that of controls (t = 2.629, p = 0.013). Compared with SHT patients (t = 1.925, p = 0.031) and normal controls (t = 2.875, p = 0.006), LVCS of OHT patients reduced while LVCS of SHT patients were lower than that of normal controls (t = 2.451, p = 0.020). LVRS of SHT patients were higher than OHT patients (t = 2.778, p = 0.008), but comparable to normal controls (t = 1.134, p = 0.266). LVLS of SHT and OHT significantly impaired in comparison with normal control. The increased LV myocardial T1 value and reduced strain were found in HT. CMR-based LV myocardial T1 and stain analysis are useful to evaluate myocardial tissue characteristic and mechanics in both overt and subclinical hypothyroidism.