The single phase n-type (Bi0.85Sb0.15)2(Te1-xSex)3(x=0.15, 0.17, 0.19, 0.21)compounds have been synthesized by melt-spinning combined with subsequent spark plasma sintering technique, and the microstructures and thermoelectric transport properties of the bulk materials have been systematically investigated. The results of field emitted scanning electron microscopy images show that the bulk materials possess refined crystalline and a large number of layered structures with the sizes from 10 nm to 100 nm, and their differences in composition and phase are detected neither from the back scattering image nor from element face distributing images of polishing surface. With the increase of content of selenium, the electrical conductivity and the thermal conductivity increase but the Seebeck coefficient decreases. Comparing with the traditional zone melted material, the samples with higher selenium content possesse higher thermoelectric optimum value ZT after 420 K and the highest ZT of the sample (Bi0.85Sb0.15)2(Te0.83Se0.17)3 can reach 0.96 at 360 K, whose ZT increases by 48% at 500 K correspondingly. In addition, the temperature of the peak ZT can be adjusted by varying the content of selenium, which is meaningful for the design and the fabrication of multi-scale or grade thermoelectric device.