The signal-to-noise-ratio (SNR) of the existing scannerless laser radar detector array is relatively low, which affects the range resolution of the system. The noise characteristics of the detector arrays were analyzed. It is pointed out that, the noise is ergodic and the SNR of range detector can be increased by using spatial domain accumulation in place of time-domain accumulation. According to this conclusion, an image processing method using the neighborhood averaging image processing method is proposed, which can improve range resolution of scannerless ladar system, specially for the scannerless laser radar/TV composite imaging system. The practical application in real system shows this method can effectively increase the range resolution of scannerless ladar system.