The interaction between fundamental mode Gaussian optical field (HG00), high-order Hermite-Gaussian optical field (HG10) and subwavelength single-metal slits is investigated by numerical simulation. It is found that under the same misalignment coupling, the HG10 light field can induce obvious unidirectional excitation of surface plasmon polariton (SPP). On this basis, a subwavelength metal slit pair structure is proposed. Numerical simulation shows that under appropriate misalignment coupling, the HG10 mode field and the subwavelength metal slit pair can induce more remarkable unidirectional excitation of SPP. By optimizing the slit pitch and incident light wavelength, the maximum split ratio reaches 2.6. The finite-difference time-domain method is used for numerical simulation in design optimization. The metal slit structure is simple and easy to prepare, and the asymmetrical excitation of SPP has the characteristics of dynamic adjustment, which has potential application value in micronanophotonic integration and nanometer measurement.