The propagation properties of Gaussian beam are directly influenced by beam quality factor M2 and the field of view of the receiver of lidar is limited mainly by the fiber core. The geometrical form factor which influences the measurement performance of the lidar system is related strictly with the transmission properties of laser beam and the configuration of the receiving system combined with the coupling fiber and the receiving telescope. This paper discusses mainly the properties of the geometrical form factor due to the beam quality factor M2 and the coupling fiber core, in order to optimize the design of the transmitter and receiver of the lidar and to improve the detection capability of the lidar. The numerical calculation shows that the coupling efficiency of the fiber is largely related with location position of fiber from the focus of the telescope and its core; and the range in which the geometrical form factor is less than one is largely influenced by M2 factor and is increased with the enhance of the value of the M2. The preliminary experiment is used to support the analysis of the influence factors on the performance for a non-coaxial lidar system.