A tunable nanosecond pulse fiber laser is demonstrated in the paper. The laser adopts the passive mode locking mechanism of the nonlinear amplifying loop mirror and a manually adjustable filter and fiber grating are added to achieve single-wavelength spectral output. The passive mode locked erbium-doped fiber laser with 430 m cavity length generates the nanosecond rectangle pulse at 465 kHz repetition rate. The tunable passive mode locked fiber laser incorporates a broad bandwidth mode locking device and a tunable filter in the cavity. The broad bandwidth mode locker is the key device for the tunable pulse output, which is based on a reflective nonlinear amplifying loop mirror. The result shows that the pulse duration and the single-pulse energy are 10.58 ns and 70.28 nJ respectively when the laser works at 1560 nm and has 400 mW pump power. The tunable range is from 1523.4 nm to 1575 nm.