The annihilation characteristics of positron in metal hydrides (LiH

MgH

2

A1H

3

and ZrH

1.9-2.0

) have been measured. The experimental results show that there is a intermediate component with shorter lifetime (0.3~0.4 ns) and very high intensity (~53%) in both MgH

2

and A1H

3

lifetime spectra. It presents that the annihilation characteriscs of MgH

2

and AlH

3

are quite different from that of LiH and ZrH

1.9-2.0

which are centainly known as ionic bond and metallic bond respectively. The measured S

H lineshape parameters of Doppler broadening decrease with decreasing Pauling electronegativity difference

while the w parameter behaves conversly. So

we suggest that there is a larger covalent chracter in MgH

2

and A1H

3

bond.