The start-up of passive mode-locking with a moving mirror was demonstrated in a Nd:glass fiber laser pumped by a single-stripe laser diode and pulses with a duration of 250 fs were generated. A relatively long fiber was used to lower the mode-locking threshold by increasing the Kerr effect in the fiber and the variation of the threshold for the start-up of mode-locking was investigated by changing the length of the fiber from 0.74 to 2 m., It was found that the restriction of the lasing spectrum using an intracavity slit was crucial for a low start-up threshold of mode-locking in a Nd:glass fiber laser.