The output characteristics of a narrow line width optical parametric oscillator with KTP as the nonlinear crystal pumped by a 532 nm wavelength all-solid-state quasi-continuous-wave Nd:YAG laser are studied. A quartz etalon is inserted into the resonant cavity to compress the output laser line width. Through theoretical analysis, the transmission spectra line width of the etalon for the idler wave within the pulsed optical parametric oscillator’s resonant cavity is estimated. Based on the calculation results, the parameters of the etalon for experimental use are designed. By inserting another KTP crystal into the optical parametric oscillator resonant cavity to perform intracavity frequency doubling on the idler, a tunable yellow laser output with a wavelength tuning range of 574.5-577.2 nm and a pm-level line width is achieved. At a repetition rate of 10 kHz and an average pump power of 30 W, the peak wavelength of the frequency doubled yellow light is 575.81 nm, with a corresponding average output power of 155 mW and a pulse width of about 35 ns. The line width at the peak wavelength is only 0.8 pm, and the beam quality factor in the x and y directions is measured respectively as 1.286 and 1.807.