Throughout the controllable analysis of rain resource in semi arid region, a kind of new water
permeability plastic membrane
was invented, based on validating small rainfall(≤10 mm/d). It can improve rainfall penetration into soil vertically, modify maximum soil
temperature, and ventilate soil, while it also can increase soil temperature and block evaporation as if conventional membrane does. The patent numbers are 97115761.8 and 98119892.9. A set of "principle of water
permeability in single direction", which includes "the principle automaticly opening closing of short crack" and "the principle of diffusion closed of short linear crack" as well as "black hole theory". The annual frequency of small rainfall was 70% in semi arid region in China and the water of small rainfall was equal to 150 mm, which had great potentiality of 4.5t per hactare land for maize. The tests covered with water permeability plastic membrane in Shanxi province in 1997 showed that: 1. There was 38.3% increase in maize yield and 1~4.5 percent points increase in soil water than conventional membrane and 103% increase in yield than no cover. 2. There was similar soil temperature between the water permeability membrane and normal membrane (PEM). 3. There was mini ventilation under the water permeable membrane. In order for validating small rainfall and preventing water from evaprating in topsoil as well as increasing yields of different crops in dry and semi arid land, at last, the prospects of water permeability membrane were pointed out.