The sudden rise in oil price in 1970s led various countries around the world to turn to renewable energy resources for electric power generation instead of fossil fuel-based power plants. Among different renewable power generations, wind and solar power plants have reached maturity and have been able to make a significant contribution to electricity supply. Tidal power plants have grown less due to high cost of investment. Hence, their share of electricity generation has been lower than that of wind and solar power plants. The potential of tidal energy is high and it is expected that tidal energy can play a key role for electricity production in the future power-system due to its accurate predictability. Two types of tidal power plants including barrage-type and current-type tidal power plants are developed for energy extracting from tides. The current-type tidal power plant generates electricity from the kinetic energy of tidal-currents in a way similar to wind-turbines, while the barrage-type tidal power plants are equipped with dam, barrage and reservoir in order to generate electricity from the potential energy of water stored in the reservoir. This paper proposes several methods for enhancing the generated power of barrage-type tidal power plants, which result in cost reduction of electricity generated by tidal power plants. At first, an optimum design procedure for calculating the optimum values of number of turbines, number of gates, sluice width, turbine tip diameter and turbine hub diameter is established based on the particle-swarm-optimization-algorithm, aiming to maximize the yearly produced energy. Then, the hourly optimum number of gates and turbines are calculated in the operation studies for maximizing the daily produced energy. Also, the utilization of hydro-pump is simulated as the third method of generated power enhancement. In addition, three operation modes of barrage-type power plants, including ebb-generation, flood-generation and double-effect generation are simulated and the best operation mode in terms of power generation is determined.