DW1000 for the two-sided ranging method

while the UWB base station is too close to the tag, and the two-sided ranging method sometimes fails to calculate the distance data and sometimes calculates the data error?The distance between base station and tag is put farther can get correct value, excuse me what reason is?

You didn’t indicate what code you are using for the two way ranging.
My system will reliably work from 10 cm (the minimum possible due to mechanical considerations) to 60 m so the issue you’re seeing isn’t a fundamental issue with the radio, it’s almost certainly a firmware issue. e.g. I did initially have issues with short distances when antenna delays were set incorrectly, this could result in a negative distance being calculated which was then thrown out as being invalid.