By means of the empirical electron theory (EET),the valence electron structures and cleavage energy(Gc) of titanium aluminides with hydrogen are calculated. The analysis shows that hydrogen embrittlement in Ti3Al results from brittle phase() transformation, and hydrogen embrittlement in TiAl results from solute hydrogen induced weakening of main bonds in the TiAl crystal cell with hydrogen, which results in a decrease of the cleavage energy, Gc. A practical method of reducing hydrogen embrittlement are proposed.