Colonoscopy is a safe and effective procedure to diagnose and treat the large bowel with the help of the flexible endoscope. This paper presents a new colonoscopy training simulator to help trainees practice and acquire the necessary skills and experiences with no risk to the patients and possibly less cost. The simulator includes a specialized haptic interface to transfer force feedback through a long and flexible tube, and graphics algorithms to display the virtual colon realistically while managing the large number of polygons. A new 2-d.o.f. haptic device with folding guides is developed to transmit large decoupled forces of the colonoscopy simulation to the user. The physicians apply a jiggling motion to the colonoscopy tube to advance the scope. This jiggling is an important skill of colonoscopy and is incorporated for the first time by using the new sensor mechanism. A colonoscope handle that shares the look, feel and functions with an actual colonoscope is developed with the necessary electronics inside. The simulator contains controllers to compensate for the inertia and friction effects, and is evaluated by physicians. New graphics algorithms including polygon reduction, navigation and collision detection are developed to compute the deformation and the corresponding reflective force in real-time.