Abstract: Long-time signal integration is an effective method to improve the detection of weak and slow small targets. However, during long time integration, the echoes of the target may exceed several range resolution cells and have Doppler frequency dispersion which makes the target echoes difficult to coherent integration. In this paper, the small target detection problem based on LTE signals is studied, the target scattering variability is introduced into the signal model and the system echo model based on LTE communication system is established. On this basis, the range migration and Doppler dispersion characteristics are analyzed. An echo coherent integration technique which is based on keystone transform and Fractional Fourier Transform (FRFT) is proposed to correct the range migration and Compensate the Doppler dispersion. And based on the typical target scattering model, the influence of target scattering characteristics on the coherent integration effect is analyzed; The simulation experiments are carried out under typical system conditions to verify the effectiveness of the proposed algorithm and analysis.