Abstract: Photoelectric direct-reading spectrometry was applied to the determination of trace amounts of calcium and sodium in cast aluminum alloys and optimum conditions for the determination were studied. The following requirements should be fulfilled in order to obtain satisfactory analytical results:① slit of the spectrograph should be adjusted to its best position by integral tracing to have the light with highest intensity passing through; ② sampling should be performed according to the rules described in GB/T 17432-2012, in order to avoid inclusion, crackles, gas holes, greasy dirt, dust, oxides and etc. on the analytical surface of the sample; ③ the prepared sample should have a smooth and clean surface; ④ argon of high purity and desirable flow should be used; ⑤ type calibration should be performed by analyzing standard sample having its values of contents of calcium and sodium very close to those of the unknown sample. Detection limits (3s) of calcium and sodium were 0.000 01% and 0.000 02% respectively. 5 CRMs of aluminum alloys were analyzed by the proposed method, giving results of calcium and sodium in consistency with the certified values, and another 3 known samples were analyzed duplicately giving values of RSDs (n=11) in the range of 1.6%-3.9%.