Abstract: This paper presents the results of experimental study of the Q-modulation feature of a Nd3+-doped single mode fiber laser.The system is composed of a CW Ar+ laser at wavelength of 5145 Å as a pumping source,a plane-concave optical cavity,a optical chopper as Q-switch inside cavity and a PIN detecto.With the system.Q-switch output power at wavelength 1.088μm, full width of power spectrum,relaxation..oscillation and the relationship of Q-switch feature with pumping power and chopping frequency are expermentally studied .It is useful for fiber sensor and long distance fiber communication.