Model test investigation on rectangular section composite micro-pile structure used for earth slope reinforcement has been performed, including the mechanical and deformation properties and pile spacing influence on anti-sliding capacity. Test results have shown the main following conclusions. For the rectangular section composite micro-pile structure and the similar soil in tests, micro-pile row spacing along the lateral load direction ranging from 4D to 6D (D is the diameter of micro-pile) can provide higher anti-sliding capacity. Active earth pressure of the first row pile is larger than that of other piles when the anti-sliding potential of composite micro-pile structure is fully developed. Relative deformation of the first row pile is larger than that of the middle and last row piles above the slip surface, while relative deformation of the last row pile is larger than that of other piles beneath the slip surface. The main failure mode of the rectangular section composite micro-pile structure can be regarded as bending failure in certain range near the slip surface.