An improved gas absorption spectrum measurement setup is proposed. A super fluoresent source (SFS) has been used to measure the infrared vibration-rotation spectrum of 2ν₃ band of H¹³C¹⁴N (HCN) molecule successfully. The configuration of double pass backward (DFB) type SFS, the molecule structure of HCN and fundamental modes of oscillation were introduced, the SFS output power was fixed at 2mW, J=0-27 rotation energy levels were excited. The flatness of spectrum is less than 1 dBm from 1525.3 to 1560.3nm, and over fifty absorption lines are measured directly without scanning and data fitting. The high brightness and wideband properties are utilized in the scheme, the structure is simpler, and the cost is cheaper than traditional measurement method, and it can be used to study the molecule fine structure in the laboratory.