To increase the content of boron in soluble polyborosilazanes (PBSZs) (the Si/B ratio should be less than 3), we introduce a successful one-pot synthesis method of a precursor by reaction with tris(dichloromethylsilylethyl)borane (TDSB), boron trichloride (BTC) and hexamethyldisilazane (HDMS) that satisfies the above conditions. The precursor was successfully transformed to SiBCN fibers by electrospinning technology. The resulting SiBCN ceramic material produced by the new route has high performance and high-temperature resistance against crystallization. Furthermore, we have analyzed the mechanism of the synthesis and ceramization of the new soluble precursor by NMR, FT- IR and TG- MS, and the high- temperature stability of the resulting SiBCN powder has been analyzed a by DTA, XRD and SEM.