Projection range of 7 MeV/u ,16,O,6+, ions implanted into CR-39 solid state track detector which is the material equivalent to biosamples is determined in the paper. Using measured data in the experiments, the projection range of the heavy ions in CR-39 (e. i. ion implantation depth) is analysed and discussed according to both etching rate ratio and statistics rule of residual range distribution. Results from the both ways are 32.5±6.2 µm and 30.5±6 µm respectively which are in agreement with each other well. The methods in the paper possess practical value to research on locating induced mutation in biosamples implanted by heavy ions.