An increase in global energy demand vis-a-vis the depletion of fossil fuel reserves on one hand, and environmental degradation and global warming due to the use of fossil fuels on the other hand are one of the challenges ahead. Hence, today one of the main challenges in all parts of the world is the supply of energy for the future. Accordingly, renewable energy sources such as biogas should be developed. One of the main sources for biogas production is biomass. Due to limitations on the availability of biomass, the substrate used to produce biogas should be carefully selected. On the other hand, due to the sensitivity of biogas production process control techniques to create stable conditions in the reactors or digesters and thus to produce permanent biogas production are important as well. In this study, an automatic control system for controlling pressure inside a continuous plug flow digester with an approximate volume of 3600 liters and the temperature of materials was developed. After installing the control system, in four separate periods, the production of biogas and methane for four different types of substrate including a combination of dairy manure and water (slurry) with a ratio of 1: 1(treatment 1), co-digestion of manure slurry and 8% used frying oil (treatment 2), co-digestion of manure slurry 10% used frying oil (treatment 3), co-digestion of manure slurry and 12% used frying oil (treatment 4). Feeding to the digester was carried out every other day and each time the same amount of material was discharged from the the digester. At each feeding and discharging stage, the substrate and the outgoing material were used to determine the pH level, total solids (TS), volatile solids (VS), ammonia and organic loading (COD). Also, the amount of gas generated at each digester discharge was recorded from a gas flow meter. Data were analyzed in SAS statistical software. Using LSD mean comparison, the significance difference of each parameter was evaluated. The results showed that the oil additive had a great influence on the production of biogas and the increase of methane content. In addition, the mean comparison of LSD showed no significant difference between the average volumes of biogas produced from the combination of three levels of oil addition to dairy manure slurry. But in the case of methane, the highest methane production of 61.9% to 61% was obtained treatment 4. The lowest amount of gas and methane produced belonged to the treatment 1. Also, the amount of methane gas produced on average for treatments 1, 2, 3, and 4 were 22.2, 78.4, 106.7 and 117.5 liters kg -1 of organic load entering the digester. According to the results of this study, the co-digestion of used frying oil with dairy manure produced the highest levels of biogas and methane. However, due to higher levels of COD produced in this co-digestion process, the environmental aspects of this operation and longer digestion durations should be considered. Keywords: Biogas, automatic control, continuous flow digestion, dairy manure, frying oil.