The invention provides a preparation method of a lanthanum ionomer. The method comprises the following steps: A), mixing water-soluble lanthanum salt with water to obtain a lanthanum salt solution; saponifying styrene-co-maleic anhydride copolymer; mixing the saponified styrene-co-maleic anhydride copolymer with the water to obtain a copolymer solution; B), mixing the copolymer solution with the lanthanum salt solution to obtain a mixture, and carrying out reaction on the mixture to obtain the lanthanum ionomer. The application also provides the lanthanum ionomer, which is obtained by carrying out reaction on the water-soluble lanthanum salt and the saponified styrene-co-maleic anhydride copolymer in the solution. The application also provides a polyvinyl chloride blend which is prepared from polyvinyl chloride, a calcium/zinc heat stabilizing agent and the lanthanum ionomer. The lanthanum ionomer prepared by the application is matched with the calcium/zinc heat stabilizing agent and is applied to polyvinyl chloride in a matching manner, and the mutual compatibility between the lanthanum ionomer and polyvinyl chloride is good; moreover, the lanthanum ionomer has double functions of toughening property and heat stability.