This is about a type of Piper laetispicum C.DC. extract and the preparation method thereof as well as the application of the extract in preparing drugs, healthcare products and food additives for treating and/or preventing diseases related to monoamine transmitters such as 5-hydroxytryptamine, noradrenaline and dopamine. The extract is obtained through impregnating or percolating at normal temperature or .ltoreq.70.degree. C., or is obtained through supercritical fluid extraction method, and in comparison with the existing reflux method, it has higher alkaloid content and higher biological activity.