Aim To observe the change of Apelin-13 in the myocardium of spontaneously hypertensive rats(SHR), and study its relationship with myocardial hypertrophy and cardiac function. Methods 4 weeks and 20 weeks of male SHR and WKY rats of clean level were selected and divided into 4 groups according to weeks and species, with 8 rats in each group. Noninvasive tail arterial blood pressure and heart mass index were separately measured; echocardiography and hemodynamic system assess were used to ventricular remodeling and cardiac function; HE staining was used to evaluate myocardial cells and arrangement; expression level of Apelin-13 and APJ in the myocardium was detected by Western blot. Results ①The expression of Apelin-13 and APJ in the myocardium of SHR was lower (P＜0.05),and 20 weeks old SHR group was more obvious than 4 weeks old SHR group (P＜0.05). ②With increasing age in SHR, the level of SBP, left ventricular end-diastolic pressure (LVEDP), heart weight/body weight (HW/BW), left ventricular weight/body weight (LVW/BW), interventricular septal thickness at diastole (IVSD) and left ventricular posterior wall thickness at end diastole (LVWPd) increased significantly (P＜0.05), and the level of left ventricular end-diastolic diameter (LVEDd), ejection fraction (EF), fractional shortening (FS) and maximal rate of the decrease of the ventricular pressure(－dp/dt_max) decreased obviously (P＜0.05); cardiomyocytes hypertrophy and myocardial arranged disorder. And compared with 4 weeks old SHR group, the above indexes changed more obviously in 20 weeks old SHR group. ③ The level of Apelin-13 in the myocardium was negatively correlated with IVSD, HW/BW, LVW/BW, LVEDd and LVEDP (P＜0.05), and positively correlated with EF, FS and －dp/dt_max(P＜0.05). Conclusions The expression of Apelin-13 in the myocardium of SHR is lower, a positive correlation with myocardial hypertrophy but a negative correlation with cardiac function, suggests it may be one of influencing factors of hypertensive left ventricular myocardial hypertrophy and cardiac function.