The invention provides a heavy metal detection device and a preparation method thereof. The device comprises a quartz crystal microbalance, and is characterized in that: polymer fibers are deposited on the electrode of the quartz crystal microbalance; a metal film is sprayed on the polymer fibers; and a sensing material is covered on the metal film. The preparation method is characterized by comprising the following steps: dissolving a spinning polymer raw material in a solvent to obtain an electrospinning material; performing electrostatic spinning by using the electrospinning material; depositing the fibers onto the electrode of the quartz crystal microbalance; spraying the metal film on the fibers; and placing the electrode of the quartz crystal microbalance in a container containing solution of the sensing material for soaking, and taking the electrode out to obtain the heavy metal ion detection device. The device has the advantages of high sensitivity and accurate and quantitative detection.