The flat-plate solar collectors (FPSCs) provide hot water for people’s daily life, and the minute heavy metals and impurities come out from inside collectors with hot water. Heavy metals have a potential impact on the environment, meanwhile, it also threatens people’s health. So it is necessary to detect the stagnant water samples of FPSCs. To improve the reliability of the test results of FPSC water samples, the ultra pure water was used for the stagnation of the FPSC. The ultra pure water was used to wash the FPSCs before stagnation to reduce the effect of pipe impurities on the results. The pipes materials of FPSC were made of TP2 phosphorous deoxy copper. The standard solution contains 21 kinds of heavy metal elements, such as As, Ca, Cu, Mg, Ni, Zn and so on. The concentration gradients of the standard solution were 0.2, 0.4, 0.8 and 1.6 mg·L-1, respectively. The blank sample and standard solution should be analyzed before testing the water sample. The water samples of different aluminum substrate FPSC (the blue-film coating, the black chromium coating and the anode oxidizing coating) were analyzed, and the content of heavy metal elements in water samples were also detected by ICP-OES method. Moreover, the best analytical spectrum of the 21 heavy metal elements were ensured by relevant parameters. The best analytical spectrum of partial heavy metal elements of the standardsolution were respectively (nm): As(188.979), Ca(317.933), Zn(206.200), V(290.880), Cu(327.393), Ni(231.604), Sb(206.836), Pb(220.353). It was shown that ICP-OES can simultaneously detect the content of various heavy metal elements in water samples accurately. The higher content of heavy metal elements in water samples, the greater the amplitude of the spectrum. There were not 12 heavy metal elements (Be, Co, Cd, Cr, Fe, Li, Mn, Mo, Se, Sr, Tl, Ti) in the water samples of three kinds of FPSCs, but 9 heavy metal elements (As, Ni, Cu, Ca, Mg, V, Pb, Zn, Sb) were detected in the same experiments. The changeable rule of heavy metal content in water samples showed that the heavy metal content increases with the FPSCs stagnation time, the heavy metal content increases to the peak value and then decreases with the FPSCs stagnation time, and then it decreases to the lower content gradually. The changeable rule of heavy metal content with the stagnation time was obtained with the analysis of the stagnant water samples of the FPSCs, and the superscalar and the excessive stagnation time of different heavy metal elements were also given too. The limit value of water quality standards for urban water supply (CJ/T 206—2005) for heavy metal elements was taken as reference, so these heavy metals elements (Cu, Ni, Zn) of water samples of three kinds of FPSCs were not more than that of the limit of the national standard. However, the contents of As, Pb and Sb in water samples of three kinds of FPSCs exceeded the limit of the standard after 8 days stagnation. The maximum superscalar of As, Pb and Sb elements were 0.007, 0.006 and 0.004 mg·L-1, respectively. And the superscalar of the As elements was the highest in the water samples of the blue-film coating collector and the anode oxidizing coating collector, and the superscalar of the Pb elements was the highest in the water samples of the black chromium coating collector. The detection results had certain reference significance to the manufacturers and the customers, and the technology of FPSC’s pipes should be further improved to reduce the precipitation of heavy metals. The research results can also provide some references for the research of the FPSC and the establishment of national standards.