In China, as a result of excessive application of fertilizers, farmland soil acidification has been accelerated in the recent decades, especially in facilitated cultivation systems, and in places where leaching is weak, secondary soil salinization could be observed. The presence of soluble inorganic salts in the soil has some significant effects on determination of soil pH(H₂O) (pH in soil-water suspension). Since pH is one of the most important parameters in evaluating soil acidification, it is necessary to study in depth to explore effects of several common soluble salts on determination of farmland soil pH (H₂O). To accurately evaluate soil acidification of cultivated lands under secondary salinization, effects of six kinds of soluble salts (Ca(NO₃) ₂, KNO₃, MgSO₄, K₂SO₄, CaCl₂ and KCl) in farmland soils (fluvo-aquic soil, cinnamon soil, paddy soil and red soil), especially in greenhouse soils, on determination of soil pH(H₂O) were explored in this study. Besides, comparison was done between four methods in effect of eliminating the effect of soluble salts, with potassium nitrate being the object of the study. The four methods were 1) replacing pH(H₂O) with lime potential, 2) using 0.01 mol L^-1 CaCl₂ instead of de-ionized water in extracting soil, 3) figuring out the effect of the soluble salt on determination of soil pH with a model first and deducting what was figured out from the value of pH(H₂O) determined, and 4) leaching out soluble salts from the soil with distilled water or 50℃ 50% ethyl alcohol solution first and then air-drying the soils for determination of soil pH(H₂O). Results show that the presence of 10 g soluble salt per kilogram soil may bring down soil pH by 0.09~0.87, and both soil electric conductivity and concentration of soluble salts are significantly related to pH and △pH (extent of the drop in pH) in a natural logarithm manner. The six kinds of soluble salts in the same soil differ quite much in effect on determination of soil pH and the sequence of the salts in terms of intensity of the effect varies with soil type and combination of salt ions in the soil. On the whole, the effects of nitrate and chloride are greater than that of sulfate, and the effect of calcium chloride higher than those of calcium nitrate, magnesium sulfate and three potassium salts. However, there is no significant difference between the three potassium salts. The effect of a kind of salts varies with soil type, and the four types of soils display a descending order of cinnamon soil > paddy soil > fluvo-aquic soil > red soil. All the four methods can be used to reduce or eliminate the effect of KNO3 on determination of soil pH. The presence of 6.9 g of potassium nitrate per kilogram soil lowers soil pH(H2O) by 0.24~0.71, or by -0.38~0.19 when the effect of the soluble salt is taken into account or eliminated. In terms of simplicity and effectiveness of the four methods, they follow an order of Method 1) > Method 2) > Method 3) > Method 4). Apparently, elimination of the effects of soluble salts on determination of soil pH can help improve accuracy of the evaluation and risk assessment of soil acidification in farmlands under secondary salinization, and contribute to formulation of reasonable effective risk controlling measures.