Stark spectroscopy(electroreflection spectroscopy) technique was applied to investigate the exciton transitions and charge transfer excitations in a Tin phthalocyanine(SnPc) polycrystalline film. A series of intermolecular charge transfer(CT) spectral bands was observed, which demonstrated the unique advantage and high sensibility of Stark spectroscopy in revealing weak CT transitions buried under strong Frenkel exciton bands. Photovoltaic action spectrum was measured for an ITO/SnPc/Al sandwiched device. The role that CT excitons played in photoconductivity was discussed.