The invention relates to the field of photoelectronic devices in optical communication, and discloses an n-i-n type electro-optic modulator, which comprises a substrate, a lower ohmic contact layer, a lower limit layer, a lower wave guide layer, an active layer, an upper wave guide layer, an upper limit layer and an upper ohmic contact layer from bottom to top. The upper limit layer and the lower limit layer are in N type doped structures. The active layer has a forbidden bandwidth Eg1 and refractive index n1. The upper wave guide layer and the lower wave guide layer have forbidden bandwidth Eg2 and refractive indexes n2, the upper limit layer and the lower limit layer have forbidden bandwidth Eg3 and refractive indexes n3, the forbidden bandwidth is in the relation Eg1>Eg3>Eg2, and the refractive indexes are in the relation n2>n1>n3. The modulation character of the electro-optic modulator can be improved.