Based on the second-order moment theory of beam propagation，the properties of Lorentz beam have been investigated. The expressions of the beam waists，the transverse divergence angle and the beam propagation factor have been presented. The transverse beam waist only depends on the corresponding beam parameter. However，the transverse divergence angle and the beam propagation factor are both determined by the two transverse beam parameters. The curves of the beam propagation factor versus the two transverse beam parameters are also given. The numerical results show that variational laws of the beam propagation factor in the x-and y-directions versus the two transverse beam parameters are apparently different，while the variational rule of the integrated beam propagation factor versus the two transverse beam parameters is the composite manifestation of the above cases. In the paraxial case，the beam propagation factor trends to a constant value of 141. With the beam waist being the same，therefore，the divergence of Lorentz beam is 1.41 times that of the Gaussian beam in the paraxial case. Accordingly，Lorentz beam is an appropriate model to describe certain laser sources with high divergence.