这位同学！
老师不得不说你了，你就不能跳过这个问题继续奋斗么？等你觉悟高了，再返回来解决这个问题，不行吗？
/*---------------------------- USART BRR Configuration -----------------------*/
  /* Configure the USART Baud Rate */
  RCC_GetClocksFreq(&RCC_ClocksStatus);

  if ((USARTx == USART1) || (USARTx == USART6))
  {
    apbclock = RCC_ClocksStatus.PCLK2_Frequency;
  }
  else
  {
    apbclock = RCC_ClocksStatus.PCLK1_Frequency;
  }
  
  /* Determine the integer part */
  if ((USARTx->CR1 & USART_CR1_OVER8) != 0)
  {
    /* Integer part computing in case Oversampling mode is 8 Samples */
    integerdivider = ((25 * apbclock) / (2 * (USART_InitStruct->USART_BaudRate)));   
  }
  else /* if ((USARTx->CR1 & USART_CR1_OVER8) == 0) */
  {
    /* Integer part computing in case Oversampling mode is 16 Samples */
    integerdivider = ((25 * apbclock) / (4 * (USART_InitStruct->USART_BaudRate)));   
  }
  tmpreg = (integerdivider / 100) << 4;

  /* Determine the fractional part */
  fractionaldivider = integerdivider - (100 * (tmpreg >> 4));

  /* Implement the fractional part in the register */
  if ((USARTx->CR1 & USART_CR1_OVER8) != 0)
  {
    tmpreg |= ((((fractionaldivider * 8) + 50) / 100)) & ((uint8_t)0x07);
  }
  else /* if ((USARTx->CR1 & USART_CR1_OVER8) == 0) */
  {
    tmpreg |= ((((fractionaldivider * 16) + 50) / 100)) & ((uint8_t)0x0F);
  }
  
  /* Write to USART BRR register */
  USARTx->BRR = (uint16_t)tmpreg;
}

至于计算公式，想必你已经弄到手了！