This study, exploiting the hypertensive population of CSPPT trial (ClinicalTrials.gov register number: NCT00794885), is intended to compare the effects of enalapril maleate and folic acid tablets versus enalapril maleate in preventing renal function decline among the patients with primary hypertension. The results from this trial may have the potential to transform current clinical and public health findings into practice in the prevention of chronic kidney disease(CKD) in China.