Variation of crystal structure of oligoclase with pressure was investigated by the approach of diamond anvil cell (DAC) and in situ micro-Raman spectroscopic measurement at room temperature and under pressures from 1.0 to 4.4 GPa. At 2.9 GPa a new peak round 517 cm-1 appeared, and a new phase was produced. Near 3.4 GPa a major discontinuity occurs in the pressure dependence of 288 cm-1 peak arising from the stretching mode of M—O, and 517 cm-1 peak disappeared, it implied that the oligoclase underwent triclinic to monoclinic phase transition completely at about 3.4 GPa. The peaks at 458 and 516 cm-1 peaks arising from flexural vibrational mode of Si—O—Si shifted linearly with the increasing pressures, the pressure-related slopes are 1.667 cm-1/GPa and 3.560 cm-1/GPa, respectively, whereas, the flexural vibrational mode of Al—O—Al at 480 cm-1 did not shifted linearly with the increasing pressures. The position of 288 cm-1 peak did not change obviously in comparision with 458, 516 and 480 cm-1 peaks, which shifted to lower frequency during decompression. The phase transition pressure of feldspar relates to the species of cation in the octatomic rings.