A Figure-9 cavity mode-locked erbium-doped fiber femtosecond laser is designed to reduce the self-starting mode-locked threshold by introducing π/2 phase-shift bias into the cavity mode-locked oscillator to meet the need for high reliability, lightweight femtosecond lasers with output power greater than 100 mW and and repetition frequency greater than 50 MHz in special application fields. The experimental results show that the stable mode-locked pulse train output with average power of 12 mW, repetition frequency of 85.89 MHz and pulse width of 249 fs is obtained at the pump power of 130 mW. The output of femtosecond pulse sequences with a average power of 113 mW and a pulse width of 107 fs is obtained by using a stage of normal dispersion backward pumped erbium-doped fiber amplifer.