Aiming at the problem of wide pulse pedestal and lower pulse energy of passively mode-locked fiber laser based on Semiconductor Saturable Absorber Mirror(SESAM), a double SESAM passively mode-locked ultrashort pulse fiber laser based on linear cavity structure was designed. Firstly, through increasing the number of SESAM, the optical pulse would pass through the SESAM repeatedly in one oscillating period in the cavity, the absorption of the absorber was improved to the pulse front and back edge, the Q mode-locked effect due to larger pump power was suppressed, contributed to pulse compression and raised the single pulse energy, the effect of the SESAM lower modulation depth on the pulse width and single pulse energy was eliminated. Secondly, the introduction of positive dispersion in the system could reduce the nonlinear effect caused by the peak power, and further improving the pulse energy. Finally, compared with the single SESAM mode locking under the same modulation depth and saturation flux, the output pulse width of the double SESAM mode-locked fiber laser shorted 35.2%, from 693 fs to 449 fs, and the single pulse energy raised 45%, from 2.92 nJ to 5.31 nJ.