An initial error conversion model of submarine-launched long range ballistic missiles was established by mathematical statistical analysis method. A platform tool error conversion model was established by platform drift principles, and other error conversion models were established by linear hypothesis method. A trajectory conversion method was proposed based on test data, error conversion models and trajectory simulation. The implementation steps of the method were elaborated. Validation and calculations show that ballistic reproduction corresponds with the experimental data, and the conversion results are consistent with the theoretical analysis.