This study aimed to determine yield and production constraints of peanut in Cagayan Valley using Decision Support System for Agro-technology Transfer; analyze yield gaps between simulated and actual yield, and provide decision support to optimize production. Simulation results using CSM-CROPGRO sub-model of DSSAT showed that highest potential yield is 2,267 kgs. / Hectare when planted in October 15 under rainfed condition. Under non-stressed conditions in the dry season, the potential yield is 4,805 kgs./ hectare planted in December 15. From 10 years of yield data, gap between farmer’s yield compared with rainfed potential ranges from 153 to 2,116 kgs./ hectare. Low rates of nitrogen application and pests and diseases were the factors causing yield gaps. The DSSAT program also captured the effect of prolonged drought in the last quarter of 2009 which resulted to underestimated yield, and the effect of warm weather in 2004 which showed lowering of potential yield by 50%. Regional analysis of peanut yields showed that central eastern part is more productive for rainfed conditions during the dry season; whereas southern part including Quirino and Ifugao is more suitable to producing peanut during the wet season due to cooler temperature.