Mechanically alloyed $TbCu_7 -type ;Sm_{12.5}Fe_{87.5-x}Ti_x$(x=0, 2.5, 5, 7.5),and their nitrides have been studied systematically by X-ray diffraction, A.C. initial susceptibility, and pulsed magnetization measurement. In this series, the volume expansion by nitriding is 5.6%~7.3%, and the increment of the Curie temperature is in the range of 21$0^{circ}C$~35$0^{circ}C$. With increasing Ti content, the remanence decreases linearly due to the substitution of non-magnetic Ti, and the coercivity decreases rapidly from 34.6 kA/cm (43.5 kOe) for $chi$=0 to 14.3 kA/cm (18 kOe) for $chi$=7.5. In the $Sm_{12.5}Fe_{87.5-x}Ti_xN_y$ series, the best magnetic properties were obtained from .7Ti7Ny series, the best magnetic properties were obtained from $Sm_{12.5}Fe_{87.5}N_y$($chi$=0) with $_iH_c$=34.6 kA/cm (43.5 kOe), $B_r=0.75 ;T, ;and (BH)_{max}=113.8 kJ/m^3$(10.9 MGOe).