The invention provides a preparation method of a flexible electrode and the flexible electrode. The preparation method includes the steps of: S1) spin-coating a rigid substrate with a PDMS layer; S2) with the PDMS layer as a flexible substrate, growing a gold film; S3) stripping the PDMS layer coated with the gold film from the rigid substrate to obtain the flexible electrode, and conducting and packaging the flexible electrode. The method is easy to achieve large-scale production, has high repeatability and can be used for detection and analysis for small molecular substances, such as NO, in cells; with the PDMS layer as the flexible substrate for growing the gold film, the preparation method is low in cost and is simple. The flexible electrode has excellent electrochemical performances and maintains excellent electrochemical behavior even after being bent for 200 times. The flexible electrode has potential in application of detection on the small molecular substances, such as NO, in cells and blood vessels, meridians and collaterals and nervous systems, and can be used for production of flexible electronic devices, such as a touch panel, an electronic skin component, a supercapacitor, etc.