Distributing control point used of straight closed traverse and using of distance measurement polar coordinates and near distance high degree level measuring method to do deformation measuring for the plugging water curtain wall.

A preliminary analysis on the unreliability of the closed traverse;

When surveying the closed traverse , sometimes there appears a kind of untrue closing phenomenon .

In the closed traverse measure,it should survey the two connected angle and adjustment at the same time.

The paper introduces a method of horizontal control survey of tunnel s exterior by adopting polygon closed traverse loop, assumed independent coordinate system , rigorous adjustment , adopting approximation to estimate the lateral error of tunnel and the calculation of precise kilometer and curve turn angles,thus the throughout accuracy of the tunnel was improved.