ACo2As2 (A=Ba, Sr, Ca) are end members of Co doped Ba-122 family. Understanding the magnetic behavior of these end members can help us to understand the magnetic properties of the whole Ba122 family. CaCo2As2 is A-type AFM, while SrCo2As2 and BaCo2As2 don't have static magnetic order. INS experiment on SrCo2As2 observes stripe-like AFM fluctuation, and the magnetic fluctuation of BaCo2As2 is still unknown. Here we propose to study the magnetic fluctuation of BaCo2As2, and finish the whole picture of the ACo2As2. Our study may shed light on the microscopic origin of the magnetism in these materials .