Ab initio calculations on the ground and valence excited states of the GaF molecule have been performed by using the internally contracted multireference electronic correlation methods (MR-CISD, MR-CISD+Q, and MR-AQCC) with entirely uncontracted all-electronic basis sets and Douglas-Kroll scalar relativistic correction. The potential energy curves of all valence states and the spectroscopic constants of bound states are fitted. It is the first time that the 12 valence Lambda-S states of GaF molecule and all of the 23 Omega states generated from the former are studied in a theoretical way. Calculation results well reproduce most of the experimental data. The effects of the size-extensivity correction and the avoided crossing rule between Omega states of the same symmetry are analyzed. The transition properties of the A (3)Pi(0)(+), B (3)Pi(1), C (1)Pi(1), and (3)Sigma(1)(+) states are predicted, including the transition dipole moments, the Franck-Condon factors and the radiative lifetimes. The radiative lifetime of the C (1)Pi(1) state of GaF molecule is of the order of nanosecond, implying that it is a rather short-live state. The lifetimes of the B (3)Pi(1) and (3)Sigma(1)(+) states are of the order of microsecond, while the lifetime of the A (3)Pi(0)(+) state are the order of millisecond. (C) 2004 American Institute of Physics.