Abstract: Coaxial gun discharge plasma is a high-temperature, high-density plasma produced by high-voltage pulsed breakdown of gas within the coaxial electrode gap. Under the coupling effect of a ~100 kA discharge current and a ~T-level self-induced magnetic field, the plasma is driven by the electromagnetic force and accelerates axially, reaching speeds of several hundred km/s and electron densities of ~10¹⁶ cm⁻³. Based on combined electrical and optical signal diagnostics, this paper systematically investigates the effects of working gas pressure, discharge voltage, and loop inductance on plasma velocity, acceleration characteristics, and density distribution. The results show that increasing the charging voltage leads to higher plasma velocity and density, while significantly shortening the acceleration time inside the gun. When the working gas pressure increases, the plasma density rises but the velocity decreases, resulting in a longer acceleration time. Furthermore, by adjusting the external loop inductance to change the discharge circuit characteristics, reducing the loop inductance increases both plasma density and velocity, and shortens the acceleration time. This study provides a reference for parameter selection and physical design of coaxial guns to obtain plasma with different characteristics.