The invention discloses a copper ion ratio type fluorescent probe based on a rhodamine derivative and a preparation method and application. The chemical formula of the fluorescent probe is C41H45N5O2.A rhodamine B hydrazide intermediate is firstly prepared, then an ethanol solution of the rhodamine B hydrazide intermediate and an ethanol solution of 1,3,3-trimethyl-2-(formylmethylene)indoline arerespectively prepared, the ethanol solution of 1,3,3-trimethyl-2-(formylmethylene)indoline is dropwise added into the ethanol solution of the rhodamine B hydrazide intermediate for carrying out a reaction, and the distillation and purification is performed to obtain the fluorescent probe. The fluorescent probe is applied to detect Cu<2+>. The fluorescent probe can specifically recognize Cu<2+>, the anti-interference ability is strong, the detection limit is low, the sensitivity is high, the fluorescent probe can be well applied to the Cu<2+> detection in the environment or organisms, and thefluorescent probe has important application values; and the preparation method of the fluorescent probe is simple, and the operability is strong.