Abstract: The influence of atmosphere infectant SO₂ on crops was studied by simulate test．The results show that under low concentration S0₂ the threshold dosage of chronic harm for“Jin85-3”and“Mianyang15”is 8．329 mg·h and 20．519mg·h，the threshold concentration is 0．043 mg／m³ and 0．122mg/m³ respectively when output of wheat decreases 5％．the fastness of wheat“Mianyang 15”is better．Under the high concentration SO₂ the critical dosage of acute harm to under age cornis 2．50mg／m³×4h，4．92mg／m³×2h and 7．38mg／m³×lh，whenits harm is seen．Thethreshold dosage of acute harm to corn is 5．90mg／m³ × 8h，6．49mg／m³ ×6h，11．80mg／m³ ×4h，15．00rag／m³×2h，and 17．O0mg／m³×1h．when the withered spot of laminae reached 5％．