An assembly structure of sun gear shaft and spline shaft of a gearbox for wind turbine, comprising: a sun gear shaft ; a spline shaft , wherein the spline shaft is a hollow shaft, one end of the sun gear shaft is inserted into the spline shaft , and the one end of the sun gear shaft inserted into the spline shaft is connected to the spline shaft through a spline pair ; a mechanical pump drive gear , wherein the mechanical pump drive gear is mounted at one end of the spline shaft , and an inner diameter of the mechanical pump drive gear is less than an inner diameter of the spline shaft ; and a distance ring , wherein the distance ring is disposed in the spline shaft , one end of the distance ring abuts against an inner side of the mechanical pump drive gear and is securely connected to the mechanical pump drive gear , and another end of the distance ring is spaced from the one end of the sun gear shaft in the spline shaft ; wherein the distance ring includes a distance ring side wall parallel to the spline shaft and a distance ring bottom perpendicular to the spline shaft ; the distance ring side wall abuts against the inner side of the mechanical pump drive gear and is securely connected to the mechanical pump drive gear ; and the distance ring bottom is spaced from the end of the sun gear shaft in the spline shaft ; characterized in that : wherein a first bolt hole is disposed at an end of the distance ring side wall connected to the mechanical pump drive gear , the first bolt hole is disposed along an axial direction of the distance ring , the mechanical pump drive gear is provided with a second bolt hole corresponding to the first bolt hole , and a first bolt is inserted into the second bolt hole and the first bolt hole so that the distance ring is secured to the mechanical pump drive gear . a sun gear shaft ; a spline shaft , wherein the spline shaft is a hollow shaft, one end of the sun gear shaft is inserted into the spline shaft , and the one end of the sun gear shaft inserted into the spline shaft is connected to the spline shaft through a spline pair ; a mechanical pump drive gear , wherein the mechanical pump drive gear is mounted at one end of the spline shaft , and an inner diameter of the mechanical pump drive gear is less than an inner diameter of the spline shaft ; and a distance ring , wherein the distance ring is disposed in the spline shaft , one end of the distance ring abuts against an inner side of the mechanical pump drive gear and is securely connected to the mechanical pump drive gear , and another end of the distance ring is spaced from the one end of the sun gear shaft in the spline shaft ; wherein the distance ring includes a distance ring side wall parallel to the spline shaft and a distance ring bottom perpendicular to the spline shaft ; the distance ring side wall abuts against the inner side of the mechanical pump drive gear and is securely connected to the mechanical pump drive gear ; and the distance ring bottom is spaced from the end of the sun gear shaft in the spline shaft ; characterized in that : wherein a first bolt hole is disposed at an end of the distance ring side wall connected to the mechanical pump drive gear , the first bolt hole is disposed along an axial direction of the distance ring , the mechanical pump drive gear is provided with a second bolt hole corresponding to the first bolt hole , and a first bolt is inserted into the second bolt hole and the first bolt hole so that the distance ring is secured to the mechanical pump drive gear . <EOS>