The intermediate temperature extended area blackbody is a wide spectral bandwidth infrared reference source. Its wavelength range covers near infrared to far infrared. As a reference source with high radiation intensity, it has been widely used in the calibration of infrared sensors such as radiation thermometers and infrared thermal imagers and in the measurement of the emissivity or transmission of samples. An extended area blackbody based on a robust structure with large emitting area is used to calibrate infrared sensors without collimators in laboratory or in the fields. To provide a solution for the performance test of infrared systems, an extended area blackbody is designed and its performance parameters are tested. The results show that the main parameters can meet the requirements of high stability and high precision.