Sound discrimination is one of important functions in auditory scene analysis. Most previous reports deal with only alarms and consider environmental sounds as a noise. However, Humans use such environmental sounds in understanding the sorrounding environment. This paper presents a sound recognition system under the assumption that user walks outdoors, and introduces methods to recognize alarms and environmental sound at the same time. This system uses two approaches. One is time domain approaches. The other is freqiency domain approaches. Considering the difference of spectrums between alarms and environmental sound,i.e. the harmonic structure of alarms, we propose a Comb-Separate-Filter(CSF) to separate alarms and environmental sounds.