The present invention discloses a sample injection device for sample collection and sample thermal desorption. The device comprises: a sample collection structure; a piston type adsorber having an adsorption cavity capable of being arranged to be in communication with the sample collection structure and configured to adsorb a sample collected by the sample collection structure; a piston cylinder defining a piston chamber that is configured for accommodating the piston type adsorber and configured to be in communication with the adsorption cavity; a thermal desorption chamber that is configured to be in communication with the adsorption cavity and the piston chamber and is configured to thermally desorb the sample adsorbed in the adsorption cavity; and a pump that is configured to be in communication with the piston chamber via a conduit and is configured to pump a sample diffused in an ambient gas into the adsorption cavity through the sample collection structure; the piston type adsorber is configured to be movable between a sample collecting position where the adsorption cavity is located outside the thermal desorption chamber and in communication with the sample collection structure so as to adsorb the sample collected by the sample collection structure and a sample desorbing position where the adsorption cavity is located inside the thermal desorption chamber so that the adsorbed sample is thermally desorbed in the thermal desorption chamber. There are also provided a method of collecting and desorbing a sample by using the abovementioned device, and a trace detection apparatus.