The invention relates to an oligochitosan and plant source substance-containing agricultural composition and applications, wherein the plant source substance is prepared by one or more of derris, tripterygium glycosides, tobacco, pyrethrum cinerariifolium, tagetes erecta, eupatorium adenophorum, radix stemonae, cayenne pepper, macleaya cordata, radix sophorae flavescentis, pyrethrum cinerariifolium, chinaberry, excoecaria sebifera, black nightshade herb, rhododendron sinensis sweet, coriaria sinica maxim, garlic, fruit of cubeb litsea tree, yellow flowered rhododendron, thymelaea, radix euphorbiae lantu, lysimachia foenum-graecum hance, peppermint, calamendiol, cortex cinnamomi, black pepper, artemisia scoparia, rhizoma alpiniae officinarum, mugwort, pepper, cynanchum komarovii, chinese honeylocust abnormal fruit, stramonium, ginko, camphora officinarum, caulis spatholobi, chinese mosla herb, herba asari, red sandalwood, erythrina indica, myrsine africana and fructus cnidii. The composition is low in people and livestock and non-target organism toxicity, fast degraded in the environment, low in residue, and free from environmental pollution. The oligochitosan and certain plant source substances in the composition are mixed and can achieve synergistic interaction, and the usage amount of the plant source substances can be reduced.