The invention relates to a production process of high-purity isoolefine (tert-olefin). When hydrocarbon mixtures which are exhausted by cracking reactors and contain isoolefine are separated, a method for absorbing low-molecular-weight ether from the hydrocarbon mixtures with water is adopted, that is, light fractions at the top of an isoolefine refining column are fully mixed with water in mixers so that a part of low-molecular-weight ether in organic phases is dissolved in water phases, then hydrocarbon-water mixtures are sent to the bottoms of washing separating columns, the organic phases mainly containing isoolefine return to the isoolefine refining column via the tops of the washing separating columns and the water phases containing the low-molecular-weight ethers and alcohols return to an alcohol fractionating column to recycle alcohol from the water phases, thus inhibiting accumulation of the low-molecular-weight ether in the system and reducing losses of isoolefine products.