In this paper, a new method to fabricate various microstructures on thermoplastics by soft lithography is demonstrated. Varied line width and varied line depth microstructures that are frequently used in micro optical products, are obtained by micromolding with simple pattern stamps. This has not been reported previously. In the new method, the variations of the line widths and depths can be adjusted by changing the side shape and the curvature of the stamp. Factors, such as temperature, pressure and the degree of crystallinity on the product qualities are analyzed. Results show that besides suitable temperature and pressure, which are important for obtaining consistent microstructures; lower crystallinity can also help for better product qualities. Optical, SEM and AFM analyses show the new method can fabricate varied line width and varies line depth microstructures with desired accuracy and features. The method proposed in this work may find potential applications in producing micro products in areas such as sensors, biochips and non-linear optical devices.