Experimental studies of soft X-ray laser for the sodium-lika recombination scheme conducted at the LF12 Laser Facility of SIOM (Shanghai Institute of Optics and Fine Mechanics) are reported. Soft X-ray amplification was observed in sodium-like copper ions by line-focused laser irradiation of slab targets. Based on the spatially-resolved measurements, the spatial distribution of the laser gain for the transition 6g-Af (72.22 A)of sodium-like copper ions was obtained, and the maximumfl of gain coefficients and gain-length produts at 500 μm from target surface were 2.0 cm-1 and 3.6, respectively. The evolution of spectrally discriminated spatial uniformity of line-shaped plasmas as lasing gain media produced by uniform laser illumination in line-focus is also in vestigated. It is found that under this expeirmental condition the line-shaped plasma is very uniform after laser heating.