Embodiments of the invention disclose a dual-mode oscillator and a multiphase oscillator. The dual-mode oscillator achieves switching two working modes through a mode switching circuit to obtain oscillation signals of two different frequency ranges. At the same time, two transformer coupled oscillators are adopted to form the dual-mode oscillator. A step up transformer in each transformer coupled oscillator multiplies the voltage amplitude of the drain electrode of a first MOS tube and injects the multiplied voltage amplitude into the grid electrode of a second MOS tube, so that the larger grid electrode voltage amplitude is obtained without increasing power supply voltage of the oscillator, thereby improving the phase noise performance of the dual-mode oscillator. The multiphase oscillator is characterized in that multiple dual-mode oscillators are connected through a multi-phase coupling circuit to form a Mobius band, multiphase oscillation signal can be generated, and the phase noise performance of the whole oscillator can be improved.