We use nonlinear polarization rotation mode-locked mechanism and high-gain-coefficient Ytterbium-doped fiber to design two new devices (polarization splitter + Faraday rotator and wave plate axis) and build a set of ultra-short cavity length mode-locked fiber lasers. And finally, the mode-locked pulse output with repetition rate of 706 MHz is realized. At the pump power of 1.5 W, the mode-locked laser can achieve laser pulse with average output power of 260 mW and pulse duration of 158 fs. The laser can operate stably for 72 h under mode-locked condition, and its structure is more conducive to miniaturization and portability for high repetition frequency systems.