Abstract: MCTGP, a new version of multi-group Monte Carlo program XIMTC, can run on the com-puter CYBER-170/825 and AST386(486) as well. It can calculate the thermal neutron flux den-sity and the thermal utilization for the triangle, rectangle or slab cell, and provide the thermalgroup contants for few groups reactor calculation. MCTGP on PC is able to show the exact graphof the calcultated cell structure.