The utility model relates to an agricultural monitoring devices specifically is photosynthetically active radiation automatic tracking measuring device in canopy, and the support is rotatory by automatic tracking apparatus control, the outer photosynthetically active radiation sensor of canopy is installed on the support top through adjustable fixed adapter, and linear photosynthetically active radiation sensor is through on the adjustable fixed adapter installing support in four canopies to be located the below of the outer photosynthetically active radiation sensor of canopy, linear photosynthetically active radiation sensor is connected with measurement controller respectively in automatic tracking apparatus, the outer photosynthetically active radiation sensor of canopy, the canopy. This measuring device adopts single -point photosynthetically active radiation and a plurality of linear photosynthetically active radiation sensor, the inside and outside photosynthetically active radiation value of automatic measure canopy, but the automatic tracking sun is rotatory, and the measurable photosynthetically active radiation who measures out in the different azels obtains multiple -point photosynthetically active radiation value.