Abstract: This invention belongs to the nanotechnology field, and discloses a nano drug delivery system with polyethyleneglycol-poly(lactic-co-glycolic acid)-poly-L-lysine (PEG-PLGA-PLL) polymer as the skeleton. The carrier can have the function of passive targeting through control of the carrier particle size. The polymer skeleton is modified through introducing side chains and specific targeting groups, so as to adjust and improve the carrier performance, and enable the carrier to have the function of active targeting. Such carrier material also has the functions of transporting active substances, tumor treatment and diagnosis, ultrasonic contrast, reversing or reducing drug resistance and so on.