Poincaré plot is an important method in nonlinear analysis of heart rate variability(HRV). Based on the modified Poincaré plot, two arguments-the regional distribution entropy and regional distribution coefficient are put forward for the quantitative description of the scatter distribution trends in the studied area. And the distributions of the Poincaré plot in the four quadrants are calculated separately. Through the analysis of the HRV sample data from healthy young people, older people and congestive heart failure(CHF) sufferers in MIT-BIH database, we find that the two parameters show a significant difference between the groups. Meanwhile, the analysis results in different quadrants show that the sensitivities of the four quadrants are different, and especially in the first quadrant, the sensitivity is best. This phenomenon shows that the changes of vagal control function are most significant between healthy people and CHF sufferers, which is consistent with previous physiological research conclusion. Experimental results also show that the method can be used for short-term data, and thus is easier to extend to clinical applications.