A new method of dynamic target distance measurement based on self-mixing speckle in an erbium-doped fiber-optic ring laser is studied. The model of self-mixing speckle measurement system is presented,and the theoretical analysis of the production of self-mixing speckle signal is also given. Through the experiments,the dynamic speckle signal is obtained. The spectrum energy density analysis is applied to the dynamic speckle signals,and a linear relationship between the spectrum energy density and the detection distance is obtained. The result shows that highly precise distance dynamic measurements can be performed by using self-mixing speckle and fiber laser.