We study Gamma-ray supernova remnant W49B and its environment using recent radio and infrared data. Spitzer IRS low resolution data of W49B shows shocked excitation lines of H_2 (0,0) S(0)-S(7) from the SNR-molecular cloud interaction. The H_2 gas is composed of two components with temperature of ∼260 K and ∼1060 K respectively. Various spectral lines from atomic and ionic particles are detected towards W49B. We suggest the ionic phase has an electron density of ∼500 cm^-3 and a temperature of

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... 10^4 K by the spectral line diagnoses. The mid- and far-infrared data from MSX, Spitzer and Herschel reveals a 151 ± 20 K hot dust component with a mass of 7.5 ± 6.6 × 10^-4 and a 45 ± 4 K warm dust component with a mass of 6.4 ± 3.2 . The hot dust is likely from materials swept up by the shock of W49B. The warm dust may possibly originate from the evaporation of clouds interacting with W49B. We build the HI absorption spectra of W49B and nearby four regions (W49A, G42.90+0.58, G42.43-0.26 and G43.19-0.53), and study the relation between W49B and the surrounding molecular clouds by employing the 2.12 μm infrared and CO data. We therefore obtain a kinematic distance of ∼10 kpc for W49B and suggest that the remnant is likely associated with the CO cloud at about 40 km s^-1.