[en] Analytical design of RETE set up a GM counter method as an analytical method of total β activity in the high level radioactive solution. To confirm the fundamental properties of GM counter, RI test was carried out by use of ⁹⁰Sr as pure β source and ¹³⁷Cs as β and γ source. Hot test of the light water reactor reprocessing liquid waste indicated that this method could be used as the analytical method of total β in the high level radioactive solution. Important results were explained as following: the detection efficiency of GM counter at γ ray 0.06 to 0.66 MeV was 0.25% or below. Its effect on the total β ray measurement was negligible. The internal conversion electron radiated from ¹³⁷Cs (^137mBa) gave positive effect on the total counter and the effect on the nuclide components in the light water reactor reprocessing liquid waste was about 3.5%. The total beta activity in the light water reactor reprocessing liquid waste was determined by this method, and the values obtained were 7.4 x 10⁹ and 8.3 x 10⁹ Bq/ml which agreed with the values by ORIGEN-2 etc. Reproducibility of the total β activity, analytical value by high dilute solution-GM counter direct method was in the range of 1.8% (RSD) that was enough to a process analytical method. (S.Y.)