An advanced optical system has been obtained to solve the problem that the traditional Wadsworth optical system can not be applied for broadband imaging spectrometer with high resolution. The meridian and sagittal focal lengths have been changed by the method of adding a cylindrical lens into the Wadsworth optical system. The optimal imaging conditions including location, inclined angle and wedge angle of the cylindrical lens have been calculated based on the analysis of the astigmatism and optical path. An example of the advanced optical system design with the working waveband of 400~800 nm has been presented to verify the theory. The results present good optical performances of the advanced system. The modulation transfer functions in all fields of view and working waveband are over 0.57, and the spectral resolution is 1.6 nm. The Wadsworth system is improved effectively.