By in situ tension observed with SEM, the deformation of hydrides and the slip behavior were investigated for the N18 zircaloy, which had been charged hydrogen by electrolytic hydrogenation method. And the effects of hydrides on the tensile properties were discussed. The results show that, the deformation of zircaloy results from multiple slip and the hydrides can be deformed evidently with matrix. The sparse strip clusters are not able to block the slip band movement, even to change the slip direction. But the big and thick strip clusters can stop the slip movement, or change the direction. The hydrides can increase the tensile strength slightly and decrease the elongation greatly. But the N18 zircaloy with 623 ppm hydrogen still has 13.1% elongation, an acceptable ductility.