Abstract: Crops are often polluted and harmed by gas.Standard on-site field technical appraisement is scientific,objective,fair and fair-minded appraisement base.The article introduced common field site technical appraisement content.It put forward the field grade procedure ,methods and technology about site check ,findings interview,to survey accident scene ,to observat plants symptoms,to discriminate and affirm pollutants and grops polluted degree,field grading and classification,grops production,loss and evaluation ,etc.