The invention discloses a device for detecting inner temperature of a rotary kiln. The device comprises a thermocouple, wherein a first end of the thermocouple can be placed into the rotary kiln to measure the temperature; a driving device, wherein the driving device is arranged at one side of the rotary kiln and the driving device is provided with the thermocouple, and the driving device can drive the first end of the thermocouple to extend into the rotary kiln; and a temperature measuring device, wherein the temperature measuring device is arranged at a second end of the thermocouple, and when the first end of the thermocouple extends into the rotary kiln, the temperature measuring device measures the second end of the thermocouple to obtain the temperature in the rotary kiln. The devicesolves the technical problem of ring forming of the rotary kiln due to too many powders in pellet production or poor temperature control in the rotary kiln in the prior art, and realizes technical effects of being capable of detecting the temperature of each place in the rotary kiln, providing basis for adjustment of burner parameters of the rotary kiln and improvement of flame shape and temperature distribution, and reducing ring forming.