Abstract: The coupling characteristics of planar Gunn nano-oscillator are studied in detail. Studies have shown that: when two oscillators are directly connected in parallel, because the interaction between Gunn oscillations is too weak for the two oscillators to operate in a common state, the amplitude of current oscillations clearly changes with time randomly. For this reason, by adding additional top-gate between the oscillators, the gate bias is used to enhance the coupling strength. Under the gate regulation, the resulting output consists of purely first harmonic oscillations with a frequency of about 0.37 THz. Based on the further analysis of the internal electron density distributions along the device channel, we find that the micro-essence of in-phase locking regime is the synchronization state of the two-channel inner domain dynamics. The coupling current amplitude is twice that of a single channel device, therefore, this structural design can improve the output power of the device.