The KKR-CPA-LDA method was used to calculate the electronic and the magnetic structures of Fe2CrGa alloy. The results indicate that Fe2CrGa alloy prefers to crystallize in Hg2CuTi-type structure rather than L21 one. The analysis of density of states reveals that the intra-atomic exchange splitting affected by crystal field plays an important role in forming the Hg2CuTi-type structure. The molecular magnetic moments measured experimentally are in a range of 2.282.48B/f.u., which is very close to that expected theoretically by the calculations based on the Hg2CuTi-type structure, but not based on the L21 structure. The experimental results also show that the Curie temperature of Fe2CrGa alloy can be continuously manipulated from 308K to 445K by heat-treating under the various conditions, indicating a high sensitivity of the exchange interaction to the atomic ordering in this system.