A self-absorption correction is important issue for the exact radioactivity determination of gamma emitting radionuclides in environmental samples which have the range of apparent density from $0.3g/cm^3$ up to $1.5g/cm^3$. In this paper, a practical and simple method without radioactive standard solutions having various densities is proposed for the self-absorption correction of environmental samples by a developed outside beaker surrounding Marinelli beaker. For the densities of 0.8, 1.0, $1.3g/cm^3$, the corrected efficiencies by the new method and the measured those by radioactive standard solutions of the three densities showed good agreement within 4 %.