An oscillator above 1 THz is designed and realized using InP-based resonant tunneling diode （RTD） and an on-chip antenna with Si-lens. The RTD model was built and studied with Silvaco software. The influences of the doping concentration of emitter， the thickness of barrier layer， space layer， and well layer on the DC characteristics of the device have been analyzed. The DC measurement of the RTD shows the peak current density J_p = 359.2 kA/cm²， the valley current density J_v = 135.8 kA/cm²， and the peak-to-valley current ratio （PVCR） = 2.64. According to the measurement， the maximum RF output power and oscillation frequency （f_max） are theoretically calculated， which are 1.71 mW and 1.49 THz， respectively. The oscillator with an on-chip bow-tie antenna and RTD is packaged with Si-lens. The measurement shows the output power is 2.57 μW at an operation frequency of above 1 THz， the DC power consumption is 8.33 mW. This is the first reported oscillator of frequency above 1 THz in domestic.