Coherent anti-Stokes Raman scattering （CARS） microscopy showed great potential for rapid pathological analysis， pharmacokinetics and other fields. However， the non-resonant background （NRB） signals generated during imaging will affect the detection of CARS signals. By tuning the wavelength， the signal can be generated at the coexistence of resonance and NRB， or at the place where there is only NRB. The influence of NRB can be eliminated to a certain extent by cancelling the two signals. In this paper， a wavelength tunable erbium-doped fiber laser system based on divided pulse amplifier and crystal frequency doubling was built. It was proposed to control the pump power of two-stage amplifiers to achieve wavelength tuning. Finally， 110.8 mW and 136 fs pulses were output at 779.1-784.5 nm， 777.5-786.1 nm and 784.5-790.5 nm. The laser and ytterbium-doped laser system can be used for CARS imaging through passive synchronization.