The invention discloses a preparation method of PEI-CDs (polyetherimide-carbon dots) capable of emitting orange fluorescence. The preparation method comprises the steps that tetramethyl benzidine (TMB) and PEI are subjected to ultrasonic treatment until TMB and PEI are completely dissolved, then the mixture is transferred into a high-pressure reaction kettle and subjected to a reaction, and PEI modified CDs are synthesized by a hydrothermal method by one step; and after the PEI modified CDs are cooled to the room temperature, an obtained PEI-CDs stock solution is dialyzed by a dialysis bag andsubjected to rotary evaporation and concentration, system polarity reduction and petroleum ether precipitation, PEI-CDs precipitates are obtained, washed and subjected to vacuum drying, and solid PEI-CDs are obtained. The synthesis technology is simple, the cost is low, the yield is high, and the post-treatment method is novel. The synthesized PEI-CDs have good water solubility, high stability and particle uniformity, emit orange fluorescence under excitation of a visible light source, have high cell safety and high cellular uptake capacity, and can effectively transmit SiRNA to cross biological membranes to enter cells.