The average mixed cluster sizes in different mixing proportions of Ar-CH4 mixed cluster and Ar-H2 mixed cluster in supersonic gas jet are studied by Rayleigh scattering method. It is found that Ar-CH4 mixed cluster could form easily when the mixed Ar and CH4 gas are used in gas jet, and the maximum cluster size is achieved when the content of Ar is 50%. The maximum cluster size of Ar-CH4 mixed cluster is larger than that of either Ar cluster or CH4 cluster. Being different from pure hydrogen cluster which only forms at liquid nitrogen temperature, Ar-H2 mixed cluster can form at room temperature. So this is the first time we have obtained hydrogen cluster at room temperature. Ar-H2 mixed cluster starts to form at H2 content value higher than 40% and it reaches maximum size when the content of H2 is 60%. Hydrogen (deuterium) mixed clusters introduce heavier Ar element on the basis of hydrogen (deuterium) clusters. It will further accelerate the deuterium ions to higher energy in deuterium cluster laser fusion experiments, so we can obtain higher neutron yield and fusion efficiency.