In this paper, an ultrasonic-assisted extraction method of cannabidiol (CBD) from hemp leaves was studied,and the CBD content in different parts of hemp was analyzed.Firstly,an HPLC analysis method for CBD was established.Meanwhile,the single factor experiment was used to analyze the effects of ultrasonic-assisted extraction power,extraction temperature,extraction time and solid-liquid ratio on the extraction yield of CBD from hemp leaf.Moreover,the Box-Benhnken experimental design was performed by using Design-expert software to determine and verify the optimal ultrasonic-assisted extraction conditions of CBD,and detect the CBD content in different parts of hemp.The experimental results showed that the Agilent HC-C₁₈ column (250 mm× 4.6 mm,5 μm),detection wavelength of 220 nm,flow rate of 1.0 mL/min,column temperature of 28 ℃,and mobile phase of 90% methanol with isocratic elution were adopted.Under these conditions,the separation effect and peak type were good,and the results were accurate,reliable and stable.The optimum extraction conditions were as follows:extraction power 320 W,extraction temperature 81 ℃,extraction time 26 min,and solid-to-liquid ratio 1∶22 g/mL.Under these conditions,the average content of CBD was 79.53±0.26 mg/g.Among the kenaf,the CBD content in the tender leaves was the highest,followed by the whole leaf,old leaf,seed and stem,and the CBD content in the root was the lowest.In conclusion,the results showed that the ultrasonic-assisted extraction was an efficient method for the extraction of CBD,and as a natural product resource,CBD has important development and utilization value.