Why is the voltage collected by stm32adc inaccurate？ - stm32

Question

I am using the STM32F103C8T6. I use the ADC for multi-channel voltage acquisition, and a potentiometer to control the voltage change. I find that the ADC value changes fluctuate. Why?
This is part of my ADC code:
uint32_t ADC_Get_Average(uint8_t ch,uint8_t times)
{
ADC_ChannelConfTypeDef sConfig;
uint32_t value_sum=0;
uint8_t i;
switch(ch)
{
case 1:sConfig.Channel = ADC_CHANNEL_1;break;
case 2:sConfig.Channel = ADC_CHANNEL_2;break;
case 3:sConfig.Channel = ADC_CHANNEL_3;break;
}
sConfig.SamplingTime = ADC_SAMPLETIME_1CYCLE_5;
sConfig.Rank = 1;
HAL_ADC_ConfigChannel(&hadc1,&sConfig);
for(i=0;i<times;i++)
{
HAL_ADC_Start(&hadc1);
HAL_ADC_PollForConversion(&hadc1,5);
value_sum += HAL_ADC_GetValue(&hadc1);
HAL_ADC_Stop(&hadc1);
}
return value_sum/times;
}
void ADC_PROC(void)
{
ADC_value1 = ADC_Get_Average(1,5) / 4096.0 * 3.3;
ADC_value2 = ADC_Get_Average(2,5) / 4096.0 * 3.3;
ADC_value3 = ADC_Get_Average(3,5) / 4096.0 * 3.3;
sprintf(adcbuff1, "V1:%.2fV", ADC_value1);
oled_show_string(24, 0, adcbuff1, 2);
sprintf(adcbuff2, "V2:%.2fV", ADC_value2);
oled_show_string(24, 2, adcbuff2, 2);
sprintf(adcbuff3, "V3:%.2fV", ADC_value3);
oled_show_string(24, 4, adcbuff3, 2);
}
enter image description here
I have tried to change the length of ADC's acquisition cycle side, but the effect is still the same, with severe fluctuations.