An all-optical passive synchronous ultrashort pulse laser source based on an all-polarization-maintaining fiber is built by the master-slave injection locking method. By optimizing the pulse energy and pulse width of pulse from the master laser, the mismatch length of 0.879 cm is achieved. The designed synchronous laser source consists of an erbium-doped fiber mode-locked pulse laser (master laser) and a ytterbium-doped fiber mode-locked pulse laser (slave laser) based on nonlinear amplifying loop mirror. The central wavelength of the master laser is 1560 nm, and its spectral width is 5.01 nm. When the output single pulse energy is increased from 0.06 nJ to 3.26 nJ, the narrowest and widest pulse widths are 221 fs and 1.79 ps after the output pulse passes through the erbium-doped fiber amplifier. The central wavelength of the slave laser is 1064 nm, and its spectral width and pulse width is 0.22 nm and 9.5 ps respectively. By controlling the output parameters of the erbium-doped fiber amplifier, the tolerance range of cavity-length mismatch between the master and slave lasers approaches to centimeter level, which provides an efficient way to avoid using the time delay control components and fiber optical path coupling components in the synchronous laser source.