Using the small-signal theory of the gyro-TWT, a pinch-point analysis based on the theory of Briggs and Bers in combination with the cold field analysis of the dielectric-loaded waveguide is employed to analysis the threshold current of the operation modes and critical oscillation lengths of the spurious mode under different load condition. The analysis concludes that the improvement in the dielectric loss, through altering the load condition can enhance the threshold current and critical oscillation length. The cold field analysis of the dielectric-loaded waveguide and a smooth waveguide dispersion relation is used to analyse the small signal gain of the dielectric-loaded gyro-TWT. The analysis gives the gain-frequency response of a dielectric-loaded gyro-TWT with the normalized background magnetic flux density B0/Bg, the thickness of the dielectric and beam current as parameters. Through the analysis of the self-oscillation and the small signal gain, the optimum operating parameters of a Kα-band dielectric-loaded gyro-TWT can be got to support the nonlinear analysis.