The output laser properties of a passive Q-switched Erbium-doped fiber laser based on a saturable absorber of single-walled carbon nanotubes coupled with a Sagnac loop is experimentally investigated. Single-walled carbon nanotube saturable absorbers are created by light deposition with a 75% transmittance. A Q-switched laser is built to modify the resonator"s Q value based on the single-walled carbon nanotubes" saturable absorption properties. When the Sagnac loop filter is placed inside the optical fiber ring cavity, the Q-switched pulses can achieve fine filtering thanks to the filtering effect produced by the Sagnac loop structure. The Q-switched laser"s operating threshold is 800 mW. The stable laser can produce a 1530.4 nm laser with an output power of 12.3 mW, repetition frequency of 210.7 kHz, corresponding pulse period of 4.76 ms, and pulse width of 2.19 ms when the pump power is 830 mW. It has a 58.37 nJ maximum pulse energy.