This invention discloses a downhole safety tool used forconcentric-tubecolumns. The tool includes an upper valve body, a main valve bodyand a lower valve body;the outer edge of the bottom end of the lower valve body is connected with the outer edge of the top end of the main valve body through an outer tube, the main valve body is provided with a valve core, and an inner cylinder is arranged in the lower valve body; the top end of the valve core is connected with the inner edge of the bottom end of the upper valve body, and the bottom end is connected with the inner cylinder; the bottom end ofthe main valve body is connected with the lower valve body; the upper valve body is provided with a central flow passage to be communicated with a central cavity body of the concentric-tuber column and a first side hole passage to be communicated with an annular cavity body of the concentric-tube column; a first liquid chamber and a second liquid chamber which are communicated with each other areformed in the upper valve body,a pilotpipeline port is formed in the top end of the second liquid chamber, and the inside of the first liquid chamber is provided with afirst plunger sliding along theaxis of the first liquid chamber.