To study the precise line profile in the mid-infrared (MIR) region, a versatile continuous wave (CW) MIR difference frequency generation (DFG) spectrometer is built up utilizing a CW Ti:Sapphire laser (700～900 nm) and a CW single-frequency 1064 nm Nd:YAG laser. The spectrometer covers the 2.5～5 μm region by tuning the frequency of the Ti:Sapphire laser. The frequency of the Nd:YAG laser is stabilized within 1×10-5 cm-1 when it is locked on the Doppler-broadened I2 absorption line near 532nm. As a result, the DFG laser frequency is stabilized to the level of 1×10-4 cm-1, which is suitable for precise line profile measurements. An absorption line of CH4 near 2927 cm-1 was recorded using this spectrometer and it presents an example for the sensitive detection with the frequency-modulation spectroscopy method.