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A numerical and optimization study has been well performed on both the circadian effect and color gamut of laser-based displays (LBDs) consisted of multiple-primary laser diodes (LDs) to realize the ultra-wide color gamut. The LBDs mainly consist of red (R), green (G), and blue (B) LDs (namely by 3-LD scheme), and also consist of red (R), yellow (Y), green (G), and blue (B) LDs (namely by 4-LD scheme). The Gaussian function is adopted to simulate the spectra of LDs due to their extremely narrow full-width at half maximum (FWHM < 2 nm). In order to evaluate the circadian effect of such LBDs, the circadian parameters, such as melanopic efficacy of luminous radiation (MELR), circadian action factor (CAF), and circadian stimulus (CS), are considered and employed in this investigation. The genetic algorithm (GA) is used to search for the optimal values of circadian parameters at a certain thresholds of color gamut. The Rec. 2020 standard is used to evaluate the color gamut, and 70%, 80%, 90%, 95%, and 100% Rec. 2020 are five selected thresholds. The optimal results are across the correlated color temperatures (CCTs) from 2700 K to 6500 K. The circadian tunablity is deduced by the ratio of the maximum MELR at 6500 K CCT to the minimum MELR at 2700 K CCT. The circadian performances are compared with the light-emitting diode (LED)-based displays. It is believed that this work could provide a useful guidance for the circadian regulation of people by the multiple-primary laser-based displays.