Abstract: The density uniformity and gradient of low density porous materials are important for its performance. β-ray detecting technology and software were constructed and used to determine the foam density uniformity with rations sensitively because existing detecting technology can not satisfy the demands of physics experiments. The systemic setting, principle and method were described. 2D and 3D graphs and statistic unevenness for the density distribution of samples were presented through detecting different technical poly 4-methyl-1-pentene (denoted as PMP or TPX) foams. Furthermore, comparing different samples, the difference of foams density uniformity was visible. The technology can not only satisfy the demands of spatial and density resolution but also achieve detecting density distribution of samples on radial and on axis non-damaging.