The present invention relates to a new preparation method for naltrexone methylbromide and intermediates thereof. The new preparation method comprises that the site 3 phenolic hydroxyl group of a starting material III is protected with chlorosilane to obtain an intermediate IV, the intermediate IV and (bromomethyl)cyclopropane are subjected to condensation to obtain an intermediate V, methylation is performed to obtain an intermediate VI, the intermediate VI is deprotected to obtain an intermediate VII, and finally ion exchange is performed to obtain naltrexone methylbromide. According to the present invention, the preparation method has advantages of short route, less by-products, high product purity, easily available raw materials, low price and low product cost, and is suitable for industrial production.