In order to resovle Quantitative Forecasting of Precision of Intersection Measure when the simple error theodolite is knowed. Beginning with the basic multi-sensor triangulation equations used to estimate a 3D target position

error propagation equations are derived by taking the appropriate partial derivatives with respect to various measurement errors. Next the concept of Gaussian measurement error is introduced and used to relate the standard deviation of various measurement errors to the standard deviation of the target 3D position estimate. Plots of the various error propagation coefficients are generated. The results indicate that the intersection errors is the smallest when the intersection angle is 90°，and when 20°-60°，the error changing is not obvious.The last is a set of equations and graphs useful for designing a two-sensor system to meet a required accuracy specification.