Abstract: Abstract: Agro-pastoral ecotone in northern China is fragile in ecology. Desertification is the prominent eco-environmental problem which is mainly induced by unreasonable land use in this area. In the background of ecological civilization construction in China, it is significant to study land suitability for cultivation in the agro-pastoral ecotone in northern China to prompt ecological protection and scientific utilization of land resource. Taking Horqin Left Back Banner as a case study, from the aspects of ecology, production and life, this paper constructed the evaluation index system to evaluate land suitability for cultivation. The results showed that the unsuitable cultivation area in cultivated land in Horqin Left Back Banner was 15 996.87 hm2 accounting for 5.339% of total cultivated land area. Owing to ecological, production and living factors, the unsuitable cultivation area of cultivated land were 7 519.23, 9 337.23 and 6 039.99 hm2 and their proportions were 40.78%, 32.84% and 26.38%, respectively. There were 6 unsuitable cultivation types including ecology; production; ecology and production; ecology and life; production and life; ecology, production and life. We reckon that unsuitable cultivation land should be de-farmed firstly in Grain for Green Project. The grass land suitable for cultivation was 197 195.94 hm2 accounting for 32.18% in total grass land area. Namely, about a third of the grass land could be reclaimed into cultivated land in Horqin Left Back Banner. However, it was found that the proportion of high quality grass land suitable for cultivation was very small from perspectives of soil suitability and topographic conditions. From the perspective of soil suitability, the most suitable, the moderate suitable and the low suitable were 26 058.42, 34 347.78, 136 789.74 hm2, accounting for 13.214%, 17.418%, 69.367% of the total grass land suitable for cultivation, respectively. From the perspective of topography condition, when the micro topography index were 1.5, 1.6), 1.6, 1.7), 1.7, 1.8) and 1.8, 1.9) ,the grass land areas were 0.18, 0, 8.1 and 277.29 hm2, accounting for 0, 0, 0.004% and 0.141% of the total grass land area suitable for cultivation, respectively. However, when the micro topography index were 1.9, 2.0), 2.0, 2.1), 2.1, 2.2), the grass land area were 82 389.24, 112 996 and 1 525.05 hm2 respectively, accounting for 41.780%, 57.301% and 0.773% of the total grass land area suitable for cultivation. From two aspects of soil suitability and topography condition, the grass land area proportion of soil suitability for most grade and micro topographic index for 1.5, 1.9) was only 0.039% to the total grass land area suitable for cultivation. And the grass land area proportion of soil suitability for most and moderate grade and micro topographic index for 1.5, 1.9) was only 0.085% to the total grass land area suitable for cultivation. In order to avoid the destruction of ecological environment and the expansion of desertification caused by the reclamation of low quality grass land, it is suggested that priority should be given to the high quality reserved cultivated land resource in reclamation and the national coordination should be maintained in cultivated land balance across provincial region.