A multiple probes scanning system comprised of two displacement sensors and one angle sensor is studied for ultra-precise profile measurement. The least squares method is applied to reconstruct the measured profile with uncertainty estimation. The parameters that influence the uncertainty associated with the measured profile are investigated. In order to obtain the optimized uncertainty, the determination of the relative parameters has been discussed in two cases. The first one is that how to select suitable sensors when intervals between two displacement sensors are known. The second one is that how to select suitable intervals between two displacement sensors when the specifications of the sensors are known. The processes of the selection in two cases are illustrated respectively according to the actual situations of the measurement.