Abstract: This paper analyses the errors of the VSWR and attenuation measured by a scalar network analyzer in terms of signal flow chart combined with the S-parameters. A formulation of the maximum error for the VSWR and attenuation of an N-port network is derived, which can be used in error analysis when measuring a microwave network. It can also be used as a reference when the microwave system designer distributes the parameters of VSWR and attenunation for each component in the network.