The wavelength-division-multiplexing passive optical network (WDM-PON) has been considered as a promising solution for future broadband access networks. The WDM-PON based on the amplified spontaneous emission (ASE) injected wavelength-locked Fabry-Perot (F-P) laser diodes has gained great attention because of its cost-effectiveness and color-free operation. The gain, side-mode suppression ratio (SMSR) and relative intensity noise (RIN) of the wavelength-locked F-P laser diode (LD) have been studied experimentally. And the relationship between injection current and the reflectivity of front facet of F-P LD, for a given ASE and gain, has been studied theoretically and experimentally. The best RIN and SMSR can be got with the injection current which is 1.3～1.7 times of threshold current. And there is an optimum front facet for a given ASE injection power and gain with the smallest injection current.