This paper presents an assessment of the impacts of introducing the greening scenario of the CAP, proposed by the European Commission as an alternative for the reformed CAP after 2013. In the past, the CAP has undergone numerous transformations in response to the changing macroeconomic environment and in reaction to developments in the farming sectors in EU countries. On the 12th of October 2011, the Commission presented a set of legal proposals designed to make the CAP a more effective policy to encourage more competitive and sustainable agriculture and vibrant rural areas. The proposal brings various new elements under consideration, some of them raising strong controversies such as introducing “greening” as a component of direct payments. Changes in the direct payments scheme in line with the EC proposition include forcing adjustments in the cropping pattern and creating ecological focus areas (EFA) on 7% of the farm land ; the consequences of such a proposal on the size and structure of agricultural production, and thus on the economic performance of farms and the whole agricultural sector are uncertain. The authors analyse historical changes to the CAP with a focus on a growing importance of the environmental component of the CAP, discuss different scenarios of shaping the direct payments system and present the results of modelling the impacts of greening the CAP on the Polish farming sector with the use of the LP optimisation model. The study was based on Polish FADN data. Results show that the majority of farmers in Poland comply with the crop diversification constraint of greening. However, establishing the required EFAs and necessary diversification on farms with simplified cropping structures will have a negative impact on the volume of agricultural production as well as on farm incomes.