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We propose and demonstrate experimentally a variable spatial pattern probe based on offset launch at the input facet of multi-mode optical waveguide for the use of optogenetics, which could generate variable spatial patterns with micron scale at the output facet of the waveguide so that the optical stimulating location in the neural tissue can be changed. By using of coupling mode theory, finite element method (FEM) and light diffusion Monte-Carlo method, we simulate their mode patterns and evolvements for TE00, TE10, TE20 and TE11 modes, excited by offset launch at different input point of the probe with core size of 17.8 × 7.8 μm2, from the output port to 50μm in the tissue. The experimental chips including array multimode waveguides with different width are fabricated using the Silica-on-Silicon processing. We selectively excite TE00, TE10, TE20 and TE11 modes in the waveguide chip with core size of 17.8 × 7.8 μm2, test their patterns and obtain their evolvements. The experimental results are coincident with the simulation results.