Red light and blue light are the main spectra of photosynthesis and photomorphogenesis in plants, and also is a developing tendency of light source in plant factory. Therefore, to realize the application of continuous light in plant factory, the response characteristics and mechanism of plants to continuous light in red and blue spectra need to be explored. The effect of continuous light and its intensity on the growth and mineral elements absorption of lettuce was investigated by ICP-AES technology in an environmental-controlled plant factory. Five lettuce cultivars were cultivated under normal light(12 h/12 h) and continuous light (24 h/0 h) in experiment 1, and grown under continuous light with five light intensity(80, 120, 160, 200 and 240 μmol·m-2·s-1) in experiment 2. The results showed that dry weights and dry weight ratios of lettuce significantly increased during 30 days’ continuous light, and increased with light intensity. However, continuous light only enhanced fresh weight in first 15 days, which also increased with light intensity. 30 days’ continuous light had no positive effect on fresh weight, even significantly reduced the fresh weight of Yidali cultivar. Compared with normal light, 30 days’ continuous light significantly reduced the Ca, Mg, Fe, Mn, Cu, and Zn contents, but slightly or significantly enhanced the accumulation of these mineral elements. Under different light intensity, the contents of Ca, Fe, Cu, and Zn decreased with light intensity, the accumulation of Ca and Fe increased with light intensity, while that of Cu and Zn were not affected by light intensity. Content and accumulation of Mg increased first and then decreased with the increase of light intensity. The content of Mn element was not significantly affected by light intensity, but the accumulation increased with the increase of light intensity. In addition, 30 days’ continuous light induced severe leaf chlorosis and necrosis, and this negative effect aggravated with light intensity, which indicated that the decrease of mineral element content aggravated the injury of continuous light to some extent. In conclusion, 15 days’ continuous light could enhance lettuce yield remarkably. However, although 30 days’ continuous light improved the dry weight, it had no positive effect on yield and induced the decrease of mineral elements contents and leaf injury. Even though lettuce plants grown under continuous light with low light intensity (80 and 120 μmol·m-2·s-1) had no leaf injury and relative higher mineral elements contents, it had no positive effect on yield. This study indicated that short-term continuous light is more suitable for the cultivation of lettuce in the plant factory, and can obtain higher yield than energy input. The decrease of mineral element content may be one of the mechanisms of long-term continuous light injury.