Hypertension caused by poor dietary habits and physical inactivity, is a risk factor for variety of cardiovascular diseases. Studies with dietary approaches to stop hypertension (DASH) have been shown to lower the blood pressure (BP) in patients with hypertension. However, reports are inconclusive on lowering the systolic BP (SBP) and diastolic BP (DBP) following DASH diet, probably due to the variances in patients’ age, body mass index (BMI) and intervention duration. Purpose: This study examined the association between DASH diet intervention and BP, and explored the influence of patients’ age, BMI and DASH diet duration on lowering the SBP and DBP. We further identified the effective variable that could potentially control the SBP and DBP in patients. Methods: PubMed, Web of Science, ScienceDirect and Google Scholar were searched for the relevant randomized controlled trials published until August 2019. Eligible trials were included according to the PRISMA (preferred reporting items for systematic reviews and meta-analyses) guidelines. Along with meta-analyses (pooled effect of DASH diet), we performed meta-regression analysis to identify the involved variables (age, BMI and DASH diet duration), and subgroup analysis to emphasize the effectiveness of each variable on changing the SBP and DBP in patients. Results: The pooled outcome of 14 trails showed that DASH diet significantly (P<0.005) decreased both SBP and DBP in patients with hypertension. Subgroup analysis results for the age factor revealed that younger adults (<50 years) represented with a significant decrease of both SBP (I2=57.3%, 95% CI: -8.91, -5.55, P=0.05) and DBP (I2=68.7%, 95% CI: -5.00, -2.58, P=0.01) following DASH diet. However, in older adults (≥50 years) only SBP (I2=63.6%, 95% CI: -5.20, -3.21, P=0.005) was decreased, not DBP (I2=35.1%, 95% CI: -2.91, -1.75, P=0.137). Furthermore, patients with higher BMI (>30 kg/m2) showed a notable decrease of SBP (I2=71.7%, 95% CI: -5.67, -3.77, P=0.000) and DBP (I2=63.2%, 95% CI: -3.08, -1.92, P=0.004), whilst patients with lower BMI (≤30 kg/m2) did not responded to DASH diet. Interestingly, shorter duration of DASH diet intervention (<12-week) effectively lowers the SBP (I2=75.1%, 95% CI: -8.87, -5.35, P=0.001) and DBP (I2=76.2%, 95% CI: -3.73, -2.05, P=0.000) in patients, but longer duration of intervention did not contributed. Conclusions: Our findings conclude that DASH diet decreases both SBP and DBP in patients with hypertension, but patients’ age and BMI are the key factors to achieve the goal. Furthermore, longer period of DASH diet intervention appears to be ineffective in controlling the BP in patients.