Abstract: Based on nature evaporation experimentation with artificial controled precipitation, two kinds of new type material for preserving soil moisture, water absorbing polymer (WAP) and water permeable plastic film (WPPF), were studied by means of orthogonal combination design. The results show that combining WAP with WPPF can strikingly increase the effects of soil water conservation.The relative importance of both measures to preserving soil moisture relate to arid process caused by the initial soil moisture and distribution of rainfall. The preserving soil moisture effect of WPPF is higher during the period of continuous drought and lower during the period of intermittent wetting and drying than that of WAP. Although the water conservation rates are of apparently difference in different arid process, their tendency is the same, that is, water conservation rate is directly proportional to the film cover rate and the amount of WAP. According to different arid process and specific requirement of preserving moisture,the optimum value region of combination measures is given under the conditions of 95% confidence degree. From the analysis of soil water availability of different treatments among three arid processes, it is shown that availability of soil water to plants during the whole circle drought is determind by water conservation measures in the period of continuous drought. To make the loessal soil water availability more than slight available level (60% field capacity) or middle available level (80% field capacity), the optimum combined measure is that the film cover rate is 67.1%～76.2%;the ratio of WAP to dry soil is 1∶673～1∶506,or the film cover rate is 92.7% ～97.3%;the ratio of WAP to dry soil is 1∶1?027～1∶424 respectively.