The invention provides a polymerase chain reaction cascade tube structure which realizes small space occupation and convenient taking and placing of a test tube. The structure comprises tube bodies and covers and is characterized in that at least two tube bodies are connected to form a cascade tube body through a tube body connecting piece; a protruding step toward an extension end is arranged at the orifices of the tube bodies at the two ends respectively; a character mark is arranged on the upper surface of the protruding step of the tube body at one end; the covers corresponding to the tube bodies in number are connected to form a cascade cover through a cover connecting piece; the covers at the two ends are respectively provided with cover panels toward respective extension ends; a corresponding character mark is arranged on the upper surface of the cover panel corresponding to the end with the protruding step with the character mark; and the cover panels cooperatively cover the corresponding protruding steps.