We present a model of an open Upper ladder type noninversion lasing system,give the steady state linear analytical solution,analyze the condition producing lasing without inversion,study the effects of the probe and driving fields detunings,exit rate,injection rates,decay rate between levels,incoherent pumping rate and Rabi frequency of the driving field on the noninversion lasing gain,dispersion and population difference by the numerical calculation results from the linear analytical solution.