The design and simulation of electron gun with required beam dynamics is done by using CST-PS software package. Geometry and position, namely axial, radial, concentricity of cathode and electrodes are the key parameters for required beam optics. The concentricity of the beam focusing electrode (BFE) is optimized with respect to the position of the cathode. Both radial and axial distances between BFE and cathode is fixed, typically at 0.2 mm for 130 mA beam current at 7 kV cathode voltage. However, it has been observed for some cases that during development of electron gun, the cathode gets tilted at its axis subsequently followed by offset of radial and axial distances of BFE. This paper presents the effect of cathode tilting on beam dynamics of the electron gun with different cathode position with respect to the BFE position and also determines its effect on helix interception current during testing of TWTs.