Abstract: CHMCK is a Monte Carlo criticality program used for complex geometrical nuclear systems.The nuclear system considered might be composed of units, each of which could be divided into several regions with different materials.The surface of the regions consist of one of conies rotating sur-faces(planes,spheres,cylinders,cones,paraboloids,ellipsoids or hyperbololds) or their combination.The axis of the rotating surface may be oritented in any manner and the surfaces may intersect with each other in arbitrary fashion.Thus CHMCK is applicable to the majority of criticality calculation.Comparing with the famous program KENO^(2,8),CHMCK has the merits of convenience and intuition for inputing and operating,due to the adopting of maximum cross section method⁽⁶⁾ in neutron transport which simplifies the program and saves the CPU time for complex geometrical.