A device and a method for analyzing an analyte in a liquid sample are provided. The device comprises a detecting chamber included in a detection device for containing a detecting element; a liquid sample transferring chamber; and a film with small pores disposed between the detecting chamber and liquid sample transferring chamber. When the detection device is inserted into a liquid sample collecting chamber, the liquid sample in the collecting chamber enters the liquid sample transferring chamber but can not enter the detecting chamber via the film with small pores. When a piston is inserted into the liquid sample transferring chamber, the piston forces a part of liquid sample in the liquid sample transferring chamber to enter the detecting chamber via the film with small pores. Using the device and the method can determine an analyte in a sample quantitatively and can complete the detection in one step.