The frequency noise of an ultra-stable laser is an important indicator for evaluating the performance of an ultra-stable laser.Generally,it is necessary to use a frequency to voltage conversion device to convert the frequency noise into voltage noise for measurement.The current frequency to voltage conversion chips on the market are suitable for the industrial control field,and cannot meet the low noise,high input frequency,and large bandwidth requirements for evaluating ultra-stable lasers.This paper designs a frequency to voltage converter with high accuracy and low additional noise based on phase-locked loop technology,introduces its working principle,and tests its conversion coefficient,accuracy and additional frequency noise.Experimental data shows that the frequency to voltage converter achieves a frequency to voltage linear conversion in the frequency range of 24.85MHz to 25.19MHz,with high accuracy.In the 100kHz measurement range,the frequency to voltage conversion error is less than 0.5dB.The frequency noise at the frequency deviation of 1Hz is less than －10dB Hz²/Hz,and the noise floor is less than －20dB Hz²/Hz in the range from 2Hz to 100kHz,which meets the requirements of ultra-stable laser frequency noise with a test linewidth of 1Hz.