One of the important factors in high radiation generation facilities is the production of a high quality electron beam. To do that, the requirements of an optical electron source, such as current, radiation emission, etc. must be met. For this purpose, cavity beam dynamics studies of 1.4, 1.5, 1.6 and 1.8-cell SRF gun were performed. In addition, detailed studies have been made on the solenoid design and the location of the solenoid along the beam path. A design with the most optimized cavity geometry and RF fields for the gun cavity was posed. The injector system was designed for the Turkish SASE-FEL project with cavities of many different geometrical sizes. The most efficient high energy cavity system is determined as 1.6-cell cavity. The emittance value of the beam was achieved as 1.76±0.42π mm mrad and the beam energy reached at the end of cavity was obtained as 3.5MeV. •Beam dynamics simulation studies have been carried out for the SRF gun system in cavities with 1.4, 1.5, 1.6 and 1.8 cells.•Astra and CST Codes were utilized to perform beam dynamic simulations and comparisons are made for all half-cell SRF cavities in many aspects to obtain optimized beam.•Simulation results of two programs are agree with each other.•Effects of the solenoid on the beam dynamics have been monitored and detailed.•Simulation results of the Superfish/Poisson and CST simulations were compared.