Lee, J. Oh, B.H. Yoon, M. MOP081 FEL radiation electron linac undulator 2015 2015-12 A bright ultrashort X-ray pulse emerges as a valuable tool for many fields of research nowadays. The single-spike operation of X-ray FEL is one way of making a bright ultrashort X-ray pulse. It requires extreme bunching and a magnetic chicane is a conventional compressor. In a low charge range, a magnetic chicane can be replaced by the velocity bunching technique. In this paper, we present the result of particle tracking simulation generating a single-spike soft X-ray SASE pulse without a magnetic chicane. We also investigate the error effects and show that this scheme is feasible under current technology.