This study numerically investigates the detailed structure and NO formation in atmospheric and high-pressure lean-premixed flames. Parallel unstructured-grid finite-volume method (FVM) has been developed to maintain the geometric flexibility and computational efficiency for the solution of the physically and geometrically complex flows. In order to realistically represent the complex turbulence-chemistry interaction of high-pressure lean-premixed turbulent flames encountered in gas turbine combustors, a flamelet model based on the level-set approach has been adopted. Special emphasis is given to the effects of pressure and equivalence ratio on the flame front location and NO formation, as well as the dimensionless parameters including turbulent Reynolds number, Re, $Damk{ddot{o}}hler$ number, Da, and Karlovitz number, Ka in the lean-premixed gas turbine-like situations. Numerical results obtained in this study suggest that the level-set approach in the context of parallel unstructured-grid FVM is capable of realistically simulating the detailed structure and NO formation in the atmospheric and high-pressure lean-premixed flames.