Corn straw biochars were prepared under 300, 500 and 700 ℃ respectively by using oxygen-limited pyrolysis method. The effects of pyrolysis temperature on the contents of water soluble, exchangeable and total base cations in corn straw biochars were studied. The amelioration effects of corn straw biochars on an acid soil and the relationships between different forms of base cations and soil acidity amelioration were studied using an indoor incubation experiment for one-year time. The results showed that pyrolysis temperature had significant effects on the contents of different forms of base cations in corn straw biochars. The contents of total K, Na, Ca and Mg, water soluble K, Na and Ca, exchangeable Ca and Mg increased with increasing pyrolysis temperature. Water soluble Mg and exchangeable K first increased and then decreased with increasing pyrolysis temperature. The main forms of K and Na in corn straw biochars were water soluble forms, about 40% Ca and 30% Mg existing in exchangeable forms, about 50% Ca and 70% Mg existing in other forms (mainly in insoluble forms). Corn straw biochar can increase acid soil pH and decrease soil exchangeable Al³⁺ significantly. The extent of increasing or decreasing increased significantly with increasing pyrolysis temperature. The sum content of total K+ total Na+ total Ca+ total Mg can be an indirect indicator for corn straw biochar’s capacity of raising acidic soil pH. The contents of soil exchangeable K, Na, Ca, Mg and total base cations were increased significantly by the addition of corn straw biochar. The total content of K or Na in corn straw biochar dominates the increase of soil exchangeable K or Na content. The content of exchangeable Ca in corn straw biochar dominated the increase of soil Mg and total base cations.