Under the special environment of airborne platform, the theoretical model is built based on probability characteristic of laser ranging, and the probability density distribution functions of pulse-echo signal envelope under different signal-to-noise ratios (SNRs) are obtained. The theoretical results show that the decrease of SNR causes different distributions of ranging data through echo wave characteristic. The experimental data present Gauss distribution with larger SNR, or Rayleigh distribution with poor SNR, or Rice distribution with general condition. According to the constant-ratio timing method, experimental results verify the rationality of theoretical model under a number of ranging data. When the ranging accuracy defined by variance is not applicable, the concept of uncertainty of measurement is introduced. Combined with the theory of uncertainty, a new method of evaluating airborne laser ranging performance is put forward. This method could overcome the unity and irrationality of traditional evaluating method, and meanwhile, it could provide an important reference for evaluating and testing airborne optoelectronic system performance.