In order to further reduce the transmission error of the helical gear pair, it is necessary to consider the composite modification based on the optimal modification scheme of the tooth profile. Table 1 shows the optimization scheme of tooth profile modification after analysis and screening.
| Programme | Modification mode | Modification amount of driving wheel（μm） | Modification amount of driven pinion（μm） | Transmission error（μm） | Hertz contact stress (N/mm2) |
| 1 | Unreformed | 0 | 0 | 0.319 | 553.412 |
| 2 | Tooth profile drum | 3 | 3 | 0.284 | 546.239 |
| 3 | Involute | 5 | 4 | 0.3 | 518.615 |
| 4 | Arc | 5 | 4 | 0.274 | 525.853 |
| 5 | Polyline arc | 3 | 3 | 0.265 | 532.917 |
| 6 | Linearity | 3 | 3 | 0.263 | 517.134 |
| 7 | Tooth profile drum | 3 | 0 | 0.267 | 477.279 |
| 8 | Tooth profile drum | 0 | 3 | 0.279 | 465.386 |
| 9 | Arc | 0 | 3 | 0.327 | 519.942 |
| 10 | Involute | 0 | 3 | 0.330 | 513.825 |
| 11 | Polyline arc | 0 | 3 | 0.330 | 529.8 |
Because the idea of composite modification is to continue to consider whether the transmission error and Hertz contact stress of the helical gear pair can be further optimized by the tooth direction composite modification based on the optimization scheme of tooth profile modification, the optimization scheme of tooth direction drum modification that can only reduce the transmission error of the helical gear pair is not listed in Table 1. The final composite modification simulation scheme is shown in Table 2.
| Programme | Tooth profile modification | Modification amount of driving wheel(μm) | Modification amount of driven pinion(μm) | Tooth modification | Modified gear | Modification range(μm) | Shaping accuracy(μm) |
| 1 | Tooth profile drum | 3 | 3 | Tooth direction drum | wheel & pinion | 3-25 | 1 |
| 2 | Tooth profile drum | 3 | 3 | Tooth direction drum | pinion | 3-25 | 1 |
| 3 | Tooth profile drum | 3 | 3 | Tooth direction drum | wheel | 3-25 | 1 |
| 4 | Involute | 5 | 4 | Tooth direction drum | wheel & pinion | 3-25 | 1 |
| 5 | Involute | 5 | 4 | Tooth direction drum | wheel | 3-25 | 1 |
| 6 | Involute | 5 | 4 | Tooth direction drum | pinion | 3-25 | 1 |
| 7 | Circular arc | 5 | 4 | Tooth direction drum | wheel & pinion | 3-25 | 1 |
| 8 | Circular arc | 5 | 4 | Tooth direction drum | wheel | 3-25 | 1 |
| 9 | Circular arc | 5 | 4 | Tooth direction drum | pinion | 3-25 | 1 |
| 10 | Broken line circular arc | 3 | 3 | Tooth direction drum | wheel & pinion | 3-25 | 1 |
| 11 | Broken line circular arc | 3 | 3 | Tooth direction drum | wheel | 3-25 | 1 |
| 12 | Broken line circular arc | 3 | 3 | Tooth direction drum | pinion | 3-25 | 1 |
| 13 | Linear | 3 | 3 | Tooth direction drum | wheel & pinion | 3-25 | 1 |
| 14 | Linear | 3 | 3 | Tooth direction drum | wheel | 3-25 | 1 |
| 15 | Linear | 3 | 3 | Tooth direction drum | pinion | 3-25 | 1 |
| 16 | Tooth profile drum | 3 | 0 | Tooth direction drum | pinion | 3-25 | 1 |
| 17 | Tooth profile drum | 0 | 3 | Tooth direction drum | wheel | 3-25 | 1 |
| 18 | Circular arc | 0 | 3 | Tooth direction drum | wheel | 3-25 | 1 |
| 19 | Involute | 0 | 3 | Tooth direction drum | wheel | 3-25 | 1 |
| 20 | Broken line circular arc | 0 | 3 | Tooth direction drum | wheel | 3-25 | 1 |