Over the past 20 years, the quality instability of medicinal herbs (QIMH) has stimulated research in the world, revealing that the crucial factors are Good Agriculture Practice and Good Manufacturing Practice. A classical view argues that QIMH controlled by these laws should have a good identical quality and the same extraction rate [1]. However, it is now clear that the considerable variation of the extraction rate among the batches caused different qualities and unstable clinical effects of the herbal extraction [2]. In this research Mendelian population firstly went forward into pharmaceutics field to steady the extraction rate of medical herbs under the controlled conditions. Based on the inter simple sequence repeat (ISSR) markers results that indicated the individual plant had genetic diversity, a Mendelian population of houttuynia cordata thunb (n) was examined through entropy of information (H). The experiments presented the results that H value ranged from 0.3656 to 0.9786, and n was 863 individual houttuynia plants, whose weight (w) was 11.22 kg if calculated as 13.0 g per individual plant. After verification tests, the several-fold n of houttuynia cordata thunb can let its extraction rate be stable. This is a novel view to stabilize the herbal extraction rate, which will contribute to a vital improvement of the classical theory.