The scale calculation for regional cultivated land fallow is an important part of the spatial allocation of the cultivated land fallow. The essence of the scale calculation is the arrangement of regional fallow space to the area of relatively low carrying capacity of the cultivated land resource in the perspective of resource carrying capacity. Based on the exploration of cultivated land fallow scale from the regional cultivated land ecological economic system, this paper selected Songtao County of Guizhou Province of the first batch of national fallow pilot counties,and this county is also a serious ecological degradation area. We applied emergy analysis and ecological footprint method to revise the improved model for the cultivated land emergy ecological footprint (EC and EF, referred to as the modified model) and the emergy sustainability index of the cultivated land (ESI_cl) for calculating the fallow area value of Songtao County in 2016. The results demonstrated that firstly, the ecological profit and loss of the cultivated land emergy can be used as a criterion for determining whether a township should be lay fallow by calculating the maximum value of fallow cultivated land area, especially for calculation of ecologically cultivated land area. Because ecological deficit of the cultivated land emergy in Songtao County has been determined by calculating ecological profit and loss of the cultivated land emergy, the cultivated land should be lay fallow totally. What's more, there are 25 townships in Songtao County, which should be lay fallow except for 3 townships. According to the statistic of county's average level (SCAL) and the statistic township level (STL), the largest fallow area is 19558.62hm² and 17673.83hm², respectively. Townships with the largest fallow area of more than medium grade are scattered in 8 townships. Secondly, ESI_cl can be used as the criterion for determining the time sequence of fallow townships. The sum of the maximum fallow area of the priority fallow townships is the minimum fallow area. Because the ESI_cl is low, the cultivated land should be moderately lay fallow in Songtao County. There are 2, 23 and 3 townships should be on priority fallow, moderate fallow, and temporary non-fallow, respectively. The smallest fallow area is 1396.10 hm² in the county, accounting for 1.88% of the cultivated land area. According to the SCAL, the range value of fallow area of Songtao County is 1396.10-19558.62hm², accounting for 1.88%-26.34% of the total cultivated land area; according to the STL, the range value of fallow area of Songtao County is 1396.10-17673.83hm², accounting for 1.88%-23.8% of the total cultivated land area. The modified model and ESI_cl provide a more scientific technical method for calculating the regional fallow area. It is expected to provide a reference for other similar regions to carry out cultivated land fallow practices.