1. Different definitions: fantasy refers to imagining unrealistic things, often for personal wishes or some special psychological reasons; Illusion refers to a fictional and unreal image or scene, which is usually caused by external stimuli or sensory illusions.

2. Different modes of production: fantasy is a kind of subjective consciousness activity, which is people's yearning for and pursuit of beautiful things, and is often not limited by objective reality; Illusion is caused by external stimuli, sensory deception or other reasons, and it exists objectively.

3. Different in essence: fantasy is an imaginative thinking activity, which can be the idea of future things or the imagination of fictional world. It is conscious and controlled by individuals' subjective; Hallucination is a wrong perception or illusion, a wrong sensory response, usually caused by external stimuli.