Since the laser,emitted by the pulsed laser,is not continuous but has an adjustable repetition frequency,the marked straight line will be discrete if the scanning speed of the galvanometer is too fast. The resolution of human eye in the clear distance is about 0.1mm,so the marked lines were divided into marked points with a pitch of 0.1 mm. The DDA algorithm was used to calculate the coordinates of each point in turn. Each point was scanned in turn through controlling galvanometer,and the stay for an appropriate time in each point make laser pulses fall on the each point. In this way,a continuous straight line can be marked. And the minimum waiting time depends on the repetition frequency of the laser and the number of laser pulses required for each point. Experiments show that this method can achieve the marking maximum speed in a given frequency,and the straight line is continuous,the depth of the line is in controllable.