The quantity and spatial distribution of cereal field are important for food security and ecology function, especially in metropolitan area. A new method was presented to design the layout of cereal field in metropolitan area and these factors were accounted for in this method such as the land productivity, the ecological function as well as the geographical location. The first step was to identify the priority assigned region (PAR) and the none priority assigned region (NPAR) according to the properties and the locations of crop lands. If the crop lands were basic farmland and they also were within the region of allowable construction, these crop lands were identified as PAR and the others were identified as NPAR. The second step was to classify the NPAR into the suitable region (SR), the optional region (OR), the unsuitable region (UR) based on the comprehensive evaluation model(CEM). As a case study, this method was applied in Pinggu District in Beijing City to optimize the layout of cereal field. The results were as follow: the area of PAR was 1427.26hm2, accounting for 11.62% of the total cultivated area, and PAR distributed mainly around the urban area and neighboring towns. The area of NPAR was 10850.96hm2 The area of SR was 4450.75hm2, with the evaluation scores higher than 85.17. SR distributed mainly in the eastern region of Pinggu District. The area of OR was 3881.18hm2, with the evaluation scores between 8000 and 8517. OR distributed mainly in the western and southern regions of Pinggu District. The area of UR was 2519.03hm2, with the scores lower than 80.00. UR distributed mainly in the northern region of Pinggu District and the topography of UR is usually mountainous. The layout method of cereal field accounting for “Production-Ecology-Location” in this paper can provide a scientific basis for the grain layout in ecological conservation area of Beijing.