An injection device is disclosed herein. The injection device is utilized to inject a liquid onto a test area of a semiconductor element. The injection device includes a base, a reservoir, a first testing pipe, a cleaning pipe and a liquid-draining pipe. The reservoir set on the base is provided with at least one connecting port and a dropping port, wherein the dropping port is against the test area of the semiconductor element. The first testing pipe, the cleaning pipe and the liquid-draining pipe are connected to at least one connecting port, wherein a first liquid is injected from the first testing pipe into the reservoir, and wherein the a cleaning liquid is injected from the cleaning pipe into the reservoir to clean the reservoir and the test area. The dropping port is utilized to drain off the first testing liquid and the cleaning liquid in the reservoir. A semiconductor testing system utilizing the injection device and its testing method are also provided herein.