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 not only fix the diode position， but also increase the matching effect， and thus solve the problem of narrow 3dB bandwidth for high-frequency band multiplier. The measured results show that the output power of the frequency tripler is all greater than 5 mW in the frequency range of 330-356 GHz. The maximum output power even reaches 11.2 mW at a driving power of 220 mW. The solid-state terahertz local oscillator， as the core device， can drive the 670 GHz sub-harmonic mixer in the superheterodyne receiver.