To achieve a steady harmonic mode-locked pulse (HMLP), the theory of rational harmonic mode-locking and the transmission characteristics of a nonlinear amplifying loop mirror were analyzed. A figure-8 shape pulse laser including an outer ring and an inner ring was constructed to theoretically and experimentally investigate the passively mode-locked technology of an erbium-doped fiber laser. By modulating the pump power to 167 mW,146 mW or 126 mW,not only a steady HMLP,but also several rational HMLPs were observed. It is found that these pulses show the same properties as those of 3th-order,5th-order,6th-order HMLPs by analyzing the repetition rate of pulse train. The reason is that the Sagnac ring in the figure-8 shape pulse laser plays the same role as the modulator used in an actively mode-locked pulse laser.