The utility model discloses a gas concentration diluting device for well logging. The gas concentration diluting device for well logging is characterized in that a sample gas flow valve, a sample gas flowmeter and a first inlet of a three-way valve are sequentially connected to one another through gas pipelines; an air flow valve, an air flowmeter and a second inlet of the three-way valve are sequentially connected to one another through gas pipelines; a control unit is respectively connected to the sample gas flow valve and the air flow valve through control lines, is respectively connected to the sample gas flowmeter and the air flowmeter through data lines and is also provided with a control signal line which is used for connection with a spectrum well logging analysis meter. According to the gas concentration diluting device for well logging, as the two inlets of the three-way valve are respectively connected to sample gas and air, the air can serve as a mixed gas for diluting the concentration of sample gas under the control of the control unit; the dilution information of the sample gas can be transmitted to the spectrum well logging analysis meter through the control signal line, therefore, the requirements on the change of concentration of the field sample gas can be met, and the reliability of well logging data is ensured. The gas concentration diluting device for well logging can be used for effectively measuring and controlling the change of concentration of the sample gas.