  This paper focuses on some properties, which include regularity, impulse,
stability, admissibility and robust admissibility, of singular fractional order
system (SFOS) with fractional order $1<\alpha<2$. The finitions of regularity,
impulse-free, stability and admissibility are given in the paper. Regularity is
analysed in time domain and the analysis of impulse-free is based on state
response. A sufficient and necessary condition of stability is established.
Three different sufficient and necessary conditions of admissibility are
proved. Then, this paper shows how to get the numerical solution of SFOS in
time domain. Finally, a numerical example is provided to illustrate the
proposed conditions.
