If she is your father's morther, 正式语：我的祖母 口语：我的奶奶 If she is your morther's morther, 正式语：我的外祖母 口语：我的外婆/我的姥姥

If the grandmother is from your mother`s side , we call her "姥姥 lǎo lao ” or "外婆wài pó”； If the grandmother is from your father`s side, we call her "奶奶nǎi nai ”.

我的外婆

我的奶奶/我的外婆

我的奶奶