Abstract: In unstable formations, the connection in multilateral hole is susceptible to deformation damage. Therefore, a multilateral connection assembly was designed. This assembly includes two pre-fab components: template and connector, which are meshed together through a trapezoid guide rail and create a continuous integrated mechanical structure. Their clearance and tolerance of match meet the requirement of hydraulic seal of the connector. Finite element simulation was used to analyze the displacement and internal stress of the connection assembly under three formation pressures, and the results showed that the amount of its deformation was very small and that its internal maximum stress was less than that of N80 steel, indicating that this connection assembly has high capacity against formation compression. This connection assembly was installed in Well He 3-Zhiping 1, verifying the reliability of this connection assembly. So it is suggested that it be further promoted and applied.