The invention relates to a fractional part measuring circuit applied to a high-resolution time-to-digital converter. The fractional part measuring circuit applied to a high-resolution time-to-digitalconverter comprises a start signal delay chain, a stop signal delay chain, a first layer signal sampling circuit, a second layer signal sampling circuit, a combination logic layer, and a one-hot codedecoding logic; the first layer signal sampling circuit is electrically connected to the start signal delay chain and the stop signal delay chain separately; the second layer signal sampling circuit is electrically connected to the start signal delay chain and the first layer signal sampling circuit separately; the second signal sampling circuit is electrically connected to the combination layer;and the combined logic layer is electrically connected to the one-hot code decoding logic. According to the invention, the differential delay line method technology, the meta-stable state and burr signal removing method by two sampling, the one-hot code generating technology, and the one-hot code decoding technology, the time interval of the picosecond level to be tested can be accurately quantified, and a precise measurement scheme for the fractional part of the large dynamic range high-resolution time-to-digital converter is provided.