Spaceborne interferometric synthetic aperture radar（InSAR）is an important method to reconstruct global dig- ital elevation model（DEM）

which measures the terrain heights using two or more SAR images from different angles.DS- InSAR is a novel radar system

which is the of combination of spaceborne SAR and satellite formation flying technology. Because of its advantage such as high DEM reconstruction precision

strong survival capability and anti-jam ability

short cycle of manufacture and low cost

the novel InSAR system has been a research hotspot in the field of spaceflight remote sensing.So far

many institutions have already proposed DS-InSAR plan with the ability of height measurement

such as interferometric Cartwheel plan proposed by CNES

interferometric Pendulum plan proposed by DLR

Radatsat-2/3 tandem plan proposed by Canada and TanDEM-X plane proposed by DLR etc. In single-baseline InSAR system

object geographic coordinates are computed from the observed ranges and Doppler central frequencies which occur when the object points are focused on SAR imaging processing.The height of object on a normal plane is generated finally.Absolute interferometric phase is needed for the above process of DEM reconstruction. However

only relative interferometric phase is obtained from phase unwrapping.So far

the effective way of converting relative interferometric phase to absolute interferometric phase requires at least one ground control point.However

it’s dif- ficult to acquire ground control points in the practical applications

which heavily restricts the application of single-base- line InSAR system. DS-InSAR system includes more than one baseline

so it is also called multi-baseline InSAR system.It offers addi- tional observation information for the derivation of position and height of object

compared to the single-baseline InSAR system.On one hand

it offers more than two ranges of information for every object ;on the other hand

it offers more than one interferometric phase difference information between every two objects.Based on the additional information it offers

this paper proposes a new DEM reconstruction approach of multi-baseline InSAR system without ground control points

So it gets rid of the above restriction of the single-baseline system.At first

theory of the approach is introduced and height measurement equations are derived.Then

error sensitivity analysis is made by first order approximation of Taylor expan- ding

which is expected to give instruction and support for the solution of DEM reconstruction equations

system analysis and error distribution etc.Its results are validated by Monte-Carlo simulation

whose results show that the above theoreti- cal error analysis method is available and can offer support for analysis and design of the system directly.