The band-to-band absorption edges of Si/Ge quantum wells were characterized by photocurrent measurement. The regular change of absorption edge was observed in different bias voltage and temperature condition. By fitting of band-to-band absorption edges,the bandgap of Si conduction band to Ge valence band was acquired. With the increase of external electric field,absorption edge curves shifted to low energy direction. By theory calculation,the relationship between the shift of absorption and external electric field was obtained,and it was well agreement with experiment. With the decrease of temperature,absorption edge shifted toward high energy direction. The qualitative analysis of this phenomena was given,and the change rate of bandgap with temperature was acquired by fitting.