Increasing global population and energy consumption has reduced the amount of non-renewable energy source and fossil fuels. Discovery of new and renewable energy sources is the best way to reduce utilizing energy resource in the world. Some of the renewable energy resources include solar energy, wind energy, thermal energy and energy released from biomass. Biomass-based primary energy sources have been increased due to the increase in food consumption, agricultural and food industry wastes and expanding husbandry industry. The increase of these wastes led generating energy from these sources to be newer and more affordable. Biogas, produced from anaerobic digestion of biomass, is a complex that contains methane (55-70%), carbon dioxide (30-45%) and a few amounts of nitrogen, hydrogen and hydrogen sulfide gases. Many researches have been done in past years on designing different systems of anaerobic fermentation, increasing efficacy of biogas production, and also increasing of methane efficiency. Experimental digesters have been produced in laboratory and semi-industrial pilot scales in universities and research institutes, and many studies have been done on performing these devices. In this research, a Continuous Anaerobic Fermentation Digester Unit (CAFDU), Plug flow piston model, was designed and made in Isfahan University of Technology (IUT), Isfahan, Iran, in semi-industrial scale, with volume of 3.6 m3. Different parts of the system include main reservoir of digester, dilution tank, control unit for material entry and exit and mixing them during a process, temperature and heating control system, control system for pressure, transmission and measurement of produced gas, and gas storage tank; all of these parts have been separately made in bio-system mechanical engineering workshop; then these parts transferred to the IUT educational and research farm and was assembled and mounted next to the farm dairy unit. To evaluate the system, 2700 liters of dairy manure diluted with water (1:1) and was fed to the digester and after 20 days and activation of metastasis microorganisms, based on a hydraulic retention time of 15 days, 180 liters of fresh diluted manure was daily fed to the digester and the same quantity was discharged from its tank. Total solids (TS) and volatile solids (VS) of the incoming and outgoing substrate were (6.76% and 4.47%), and (3.67% and 2.66%) respectively. This shows a decrease of 46% for TS and 40% for VS. The pH level increased from 6.9 to 7.7. Gas production in the first 20 days was 3435 liters, containing 58.2% methane, 38.5% CO2 and 3.3% H2S and other gases. After the starting to inject fresh fertilizer within four days, 970 liters of biogas was produced, containing 61.4% methane, 36.6% CO2 and 2% other gases. Keywords: Biogas, Methane, Continuous Digester, Anaerobic Digestion, Plug Flow Digester.