Abstract: This paper presents a large current broadband pyroelectric infrared detector optimal design method.The analysis of the pyroelectric response of the output voltage based on the combination of the characteristics of thermal radiation detection,put forword a new simulation model,and the actual circuit is basically consistent with simulation data.Through using bipolar JFET（BJFET） and changing the time constant and so on,we will improve the low-output and narrow bands which were the key issues of pyroelectric preamplifier.