The invention discloses a method for improving a coaxial-cavity dielectric oscillator. The method is characterized by comprising the following steps: reducing the output frequency of the coaxial-cavity dielectric oscillator to the half in a normal state; accessing the reduced output frequency to a high-pass filter and selecting second harmonics of the reduced output frequency; increasing the length of a resonator by three times than a quarter wavelength mode. The method has the advantages that the adjustment is more convenient and the operability is higher; the frequency variation is small, so that the difficulty in circuit debugging is greatly reduced.