In order to study the effects of amino acid chelated selenium fertilizer on selenium content and speciation in rice grain，a field experiment was carried out with the rice variety Thyme 139 as the material. Exogenous selenium application with different concentration gradients were set up，and the leaf surface sprayed with amino acid chelated selenium was carried out in the fracture stage of rice. The leaves of rice was sprayed with 13.5 g/hm² of exogenous selenium(calculated as selenium)at five different growth stages，i.e. jointing booting stage，beginning heading stage，flowering stage，grouting stage and wax-ripening stage. The selenium content in different tissues and organs of rice and grain selenium speciation were measured and analyzed in the mature stage. The result showed that sprayed with amino acid chelated selenium increased the content of selenium in different tissues and organs of rice，the selenium content in rice organs increased with the increase of sprayed selenium concentration within the proper range. Selenomethionine(SeMet)was the main form of selenium in rice grains，and the variation of SeMet content in rice grains was consistent with that of total selenium content. The selenium content in rice grains was 0.168，0.431 and 0.439 mg/kg when treated with 6.75，13.5 and 27.0 g/hm² of exogenous selenium，respectively，which reached the local standard of selenium-rich agricultural products in Guangxi，Classification Requirements of Selenium Content in Selenium-rich Agricultural Products(DB45/T 1061-2014). The selenium content in rice grains increased with spraying selenium from the jointing booting stage to the grouting stage，the highest selenium content in rice grains was 0.320 mg/kg which appeared at the selenium treatment sprayed at the grouting stage. The content of SeMet in rice grains accounted for 43% ～ 91% of the total selenium content，the ratio of SeMet content to the total selenium content in rice grains showed:the jointing booting stage>the beginning heading stage>the flowering stage=the grouting stage>the wax-ripening stage. The ratio of SeMet decreased with the period of selenium application closer to the maturity of rice，showed that the transformation time of selenium in rice leaves had a significant effect on the speciation of selenium in rice. Early spraying of exogenous selenium at rice growth period was beneficial to the formation of organic selenium and increased the proportion of organic selenium in rice grains. In this study，the application of selenium bioaugmentation in the production of selenium-rich rice，and the optimal amount of amino acid chelated selenium sprayed on the leaves of selenium enriched rice at the break stage was 13.5 g/hm². By spraying 13.5 g/hm² of amino acid chelated selenium at five different growth stages could produce selenium-rich rice，and the best spraying time of exogenous selenium was at the grouting stage.