561 nm laser output is achieved from LBO intra-cavity frequency doubling of a laser in which NdYAG is end-pumped by LD. Using the 2 mm×2 mm×10 mm LBO crystal with type-Ⅰ phase matching cutting, the 561 nm laser output power is 123 mW when the pump power is 5 W. The conversion efficiency of 2.46% is obtained. The frequency-doubled light waves of 556 nm and 558 nm easily appear in experiment. From the influence of nonlinear conversion efficiency on fundamental-frequency light oscillation, the reason of 1112 nm and 1116 nm line oscillation is analyzed. As a contrast, we carry out the same experiment using a 2 mm×2 mm×8 mm KTP crystal with type-Ⅱ phase matching cutting. Results show that the laser is easy to realized 561 nm single spectral-line laser. The experimental results and theoretical analysis are consistent with each other.