Enzyme F1-ATPase catalyzes the hydrolysis of ATP and converts chemical energy into mechanical rotation with exceptionally high efficiency. It performs cellular functions like a rotary energy-transducing molecular motor and thus promises unique applications in nanobiotechnology. To better understand the operating mechanism and chemomechanics of F1-ATPase, we propose a simulation model based on the binding-change schemes, enzyme kinetics and Langevin dynamics. We show that the torsional energy and stepwise rotation can be regulated by a series of near-equilibrium reactions when ATP molecules are hydrolyzed. An effective 'ratchet' drag is also derived to account the motor's unidirectional spin. Complex schemes of binding-changes may exist in the F1-ATPase motor at different operating conditions. The chemomechanics described in this work is of fundamental importance to all ATP-fueled motor proteins.