The invention relates to an instrument-free nucleic acid extraction device and a trace nucleic acid extraction method. The trace nucleic acid extraction device comprises a tubular main body 1, wherein one end of the tubular main body is provided with a joint 2 connected with a suction device and the other end of the tubular main body is provided with a plug 3; and a filter element device 4 for combining nucleic acid is arranged inside the tubular main body or the plug. The trace nucleic acid extraction device replaces a high-rotating speed centrifugal machine, can achieve good separation effect in a heterogeneous liquid phase system, is low in cost, easy to operate and short in operating time, and can be widely applied to rapid nucleic acid diagnosis in primary hospitals and emergency rooms under relatively bad experiment conditions. A nucleic acid detection method is a simple means of extracting a biological sample of nucleic acid, the purity of the extracted sample meets the requirement on nucleic acid amplification, other instruments are not needed, the device is used at one time, and the method can be widely applied to extracting pathogen or host nucleic acid, and is used for clinical detection and diagnosis.