Benin is predominantly an agricultural country which accounted for 39% of GDP with 70% economically active population in the agricultural sector, that year. Small, independent farmers produce 90% of agricultural output, but only about 17% of the total area is cultivated, much of it in the form of collective farms since 1975. Benin with subtropical climate have enough water resources and land facilities to growth and be one power agriculture country but the sector is plagued may many problem such as lack of infrastructure, poor utilization of rural credit, and inefficient and insufficient use of fertilizer, insecticides, and seeds. Those problems have a big effect on agriculture income and rural household income and the high poverty rate.This is contract between resources potentiality and poor living condition. However the manly source of those problems maybe the lack on public expenditure in this sector. The purpose of this research is to evaluate how the low public expenditure has impact on the agriculture growth and poverty rate. To evaluate that, we first made a theory approach of the impact of agriculture growth and poverty reduction by presentation the model of model elaborate by KAWALI and son in 2006 to evaluate the contribution of public expenditure to achieve MDG b agriculture grows. The application of this model on Benin agriculture show Benin need the annual Agriculture expenditure required for 2004-2015 is 356 Million USD( 8,1% agriculture growth per year) with the conservative scenario beside 301 Million USD (7,1% agriculture growth per year) with optimistic scenario. However the analysis of agriculture public expenditure in Benin is very low( lower than 10% of the GDP) and the public expenditure general is lower than 25% of GDP (lower than 25% that is recommend by best practice) and the high rate is in military not in growthing sector. This lack of sufficient public agriculture expenditure is felt at upriver and backing of the agriculture sector. This is justifying by the agriculture production surplus management problem in this year. This is du to inability of crops stocking, crops conservation system lack and crops distribution system lack due to (infrastructure lack) and insufficient investment lack. The importance of public expenditure is become more and more a crucial problem and news policies should be elaborated and focus in major parties of public expenditure in economic growth sector that is agriculture in Benin because with climate change negative effect the situation will be more degradation and rural poor population will be increase faster.