Based on the hybrid integration method, a 335 GHz unbalanced frequency tripler is designed with a symmetrical tapered gradient line matching structure. Under the condition of ensuring single-mode transmission, the matching structure can increase the matching effect while fixing the position of the diode, and improve the problem of the narrow 3 dB bandwidth of the high-frequency band multiplier. The measured results show that the output power of the frequency tripler is greater than 5 mW in the frequency range of 330-356 GHz. The maximum output power is 11.2 mW at a driving power of 220 mW. The solid-state terahertz local oscillator composed of it as the core device can drive the 670 GHz sub-harmonic mixer in the superheterodyne receiver.