The variation of energy and water exchange between land surface and atmosphere, the influence on atmospheric temperature and humidity at 2m height, soil moisture at four layers (10cm, 30cm, 60cm, 100cm)， and surface/underground runoff under different irrigation schedule from 20 July to 30 July, 2002 were analyzed on oasis in arid region of NW China and simulated using the non-hydrostatic atmospheric mesoscale model MM5, in which the land surface process parameterization (OSU LSM) was involved and soil layers, vegetable layer, hydrological process and snow were included. The horizontal resolution was selected as 1km. We knew from “Numerical simulation of Oasis’ Environmental influence under different quantity irrigation in arid regions of Northwest China” that 500m3/hm2/10d is a proper volume for later dekad of July,2002. We determinate the best irrigation schedule based on the method of keeping soil moisture steady. The results showed that: firstly, soil volumetric water content fell down gradually when irrigating 50m3/hm2/d every two days or every several days. Soil moisture could not keep in a stable range, and could not provide steady water supply for the plant growth. So this irrigation schedule is not a proper one for later dekad of July in oasis. Secondly, the surface runoff of irrigation schedule is smallest when irrigating ten days evenly and the quantity is 50m3/hm2 every day. Soil moisture variation of it is smallest also among the following three schedules: irrigating ten days, and 50m3/hm2, every day; 100m3/hm2/d, every two days; and 250m3/hm2/d, every five days. So the first schedule is the best scheduling according to the irrigation schedule determination method from soil moisture maintenance. But it is difficult to realize because of a series of problems such as equipment and labors. Then, the most similar schedule can be adapted in real life. In one word, the shorter the interval between irrigations under the given irrigation quantity crops need every time, the better. So the irrigation water can be transformed to soil moisture as soon as possible to supply crops on it, not to flow down along the slope of topography as surface runoff. So we’d better irrigate as the best irrigation schedule so as to hold the limited water resources.