Since previous studies of parallel mechanisms (PMs) have tended to favor symmetrical overall configuration to obtain relatively stable kinematic and dynamic performance and to satisfy isotropic requirements. The analysis of kinematic and dynamic performance of asymmetric mechanisms has been an issue of interest. In this paper, an asymmetric SCARA-type PM with 4 degrees-of-freedom (DOF) is proposed. First, the orientation characteristic set is calculated to obtain the DOF of the PM. Then, the inverse kinematics and the velocity and acceleration of each branch chain of the mechanism is analyzed. The dynamic model of the mechanism is established according to the principle of virtual work. The workspace of the mechanism is drawn according to the constraints that have been given to the mechanism's kinematic pairs. The singularity, dexterity, motion/force transfer performance and maximum acceleration performance of the mechanism are also analyzed. On this basis, the kinematic and dynamic performance evaluation indexes of the mechanism are studied. Finally, the workspace and acceleration performance of the mechanism are optimized based on the differential evolution algorithm (DE) to obtain the structural parameters when the mechanism achieves optimal performance. The asymmetric PM proposed in this paper, as well as the algorithm of performance index and optimization method used can provide some reference value for configuration design and optimization analysis.