Laser is focused on soil samples doped with Cr and Cu elements. Signal-to-background ratio (SBR) of Cr (I) 425.435 nm, 427.481 nm and Cu (I) 324.754 nm, 327.396 nm is analyzed. The calibration curve is drawn using the intensity ratio of each line to the Fe reference line intensity, and the limit of detection is calculated. The effect of atomic configuration, angular momentum and transition probability on calibration curve and limit of detection is studied. It is indicated that the high SBR spectral line gets lower limit of detection, and is more sensitive to element detection. The spectral line SBR is independent on transition probability. The variation in SBR with element content exhibits similar characteristics for the lines with the same atomic configuration. The excitation of lines with large angular momentum is better with higher regression coefficient of calibration curves. The limit of detection of Cr (I) 425.435 nm (4-3) and Cu (I) 324.754 nm (3/2-1/2) decreases by 11% and 42% compared to the lines Cr (I) 427.481 nm (3-3) and Cu (I) 327.396 nm (1/2-1/2) respectively. The lines with large angular momentum are more sensitive and more suitable for element detection.