The multi-screen optical method is put forward to solve the problem of three-direction coordinate measurement when the flying projectile gets close to object and explodes in the high altitude. According to experiment characteristic, the demerits of multi-screen across target are pointed out and the technology of using lateral layout area camera to assistant multi-screen across target is studied. The mathematics geometry model on camera, simulating object and multi-screen across target is set up based on projectile burst image acquired by lateral camera. The lateral coordinates calculation method and the modified principle of two-dimensional coordinates of multi-screen across target are studied and analyzed by using projectile flying contrail and its plane coordinates of burst image. The function of three-dimensional projectile burst coordinates is given. The differential method is applied to analyze their coordinate′s errors, which come from the angle of intersection screen, the thick of screen, the measurement time, ranging and so on. Coordinate errors will be less than 40 mm when the height of simulating object is less than 50 m by theoretical analysis and calculation.