The dispersions of joint estimation of the parameters of harmonic signal are presented in the article. Array’s sensors receive the signal at the background of non-Gaussian interference. It’s presumed, that estimation are calculated by the method of polynomial maximisation for order equal to S = 1, 2, 3, 4. It’s shown that for non-Gaussian interferences the dispersions of joint estimations can be significantly smaller than the dispersions of estimations in the case of Gaussian interference.