This paper designed, fabricated and measured a THz fourth-harmonic conversion system based on GaAs Schottky barrier diode. Using the fourth-harmonic mixing method, the LO frequency is a quarter of (RF-IF) frequency and is corresponding to W band. Furthermore, the generators only need to supply LO signal of Ku band and IF signal of C band due to the sextupler in LO chain and quadrupler in IF chain. Based on the measurement results, this conversion system could generate 364-380 GHz signal with a typical conversion loss of 25.5 dB. The presented conversion system extends the existing microwave generators to THz applications and offers a low-cost, simple and alternative solution for those who lacking of lower THz signal source.