In the present paper, the spectral properties of two-dimensional (2D) photonic crystal quantum well structures were studied numerically. The structures consist of a 2D photonic crystal (PC) with square lattice of parallel dielectric circular columns in air and some middle layers of columns are removed. Similar to the electrons in semiconductor quantum wells, the photonic bandgap (PBG) in PC can act as a potential barrier to photons, which gives rise to quantized photonic states in the PBG region. Photonic band structures were calculated using plane wave expansion method and transmission spectra were obtained using transfer matrix method. The results show that discrete transmission peaks appear in PBG region. More transmission peaks arise with the increase of the well layer and the strength decreases with the increase in the potential layer width. The relationships between the frequency of transmission peaks and the width of well layer were also discussed.