A brand new direct and adaptive slicing approach is proposed, which can apparently improve the part accuracy and reduce the building time. At least two stages are included in this operation: getting the crossing contour of the cutting plane with the solid part and determining the layer thickness. Apart from usual SPI algorithm, slicing of the solid model has its special requirements. Enabling the contour line segments of the cross-section as long as possible is one of them, which is for improving manufacturing efficiency and is reached by adaptively adjusting the step direction and the step size at every crossing point to obtain optimized secant height. The layer thickness determination can be divided into two phases: the geometry-based thickness estimation and the material-based thickness verifying. During the former phase, the geometry tolerance is divided into two parts: a variety of curves are approximated by a circular arc, which introduces the first part, and the deviation error between the contour A brand new direct and adaptive slicing approach is proposed, which can apparently improve the part accuracy and reduce the building time. At least two stages are included in this operation: getting the crossing contour of the cutting plane with the solid part and determining the layer thickness from the solid model has its special requirements. The effect of forming a solid model has its special requirements. Enabling the contour line segments of the cross-section as long as possible is one of them, which is for improving manufacturing efficiency and is reached by adaptively adjusting the The layer thickness determination can be divided into two phases: the geometry-based thickness estimation and the material-based thickness verification. During the former phase, the geometry tolerance is divided into two parts: a variety of curves are approximated by a circular arc, which introduces the first part, and the deviation error between the contour