The invention relates to a chloride ion measuring method of leveling liquid that is used in steel plate rolling, which is implemented according to following steps: firstly, a certain amount of the leveling liquid sample to be measured is placed into a porcelain crucible which is placed into a baking oven for drying; secondly, the dried sample is placed into a retort furnace so as to be cauterized, and then taken out and cooled; thirdly, the sample that is processed by the second step and the crucible are rinsed by secondary distilled water, rinsed liquid is added into a sample solution until a certain volume value is reached, and ultrasonic oscillation is used for dissolving the chloride ions of the sample in the water; fourthly, a certain amount of the solution that is processed by the oscillation and contains the chloride ions is filtered by a filter paper, a filtered solution is collected, the chloride ion content in the filtered solution is measured by the Mohr volumetric method, and simultaneously a same amount of the secondary distilled water is used for blank titration, and the final chloride ion content in the leveling liquid can be obtained by computation. The chloride ion measuring method of the invention has the advantaged of simplicity and low test cost.