<p>Gifford-McMahon-type pulse-tube cryocoolers (GM-PTCs) working at liquid helium temperatures are promising in quantum technology and cryogenic physics for their high reliability and minimal vibration. These features stem from the fact that there are no extra moving parts introduced into the system. The rotary valve is a key component in GM-PTCs that transfers the output exergy from the compressor to the cold head. Because a low Carnot efficiency of 1.58% is achieved at liquid helium temperatures, optimizing the rotary valve is crucial for improving the efficiency of GM-PTCs. In this regard, an exergy-loss analysis method is proposed in this paper to quantitatively obtain the leakage loss and viscosity loss of a rotary valve by experimental measurements. The results show that viscosity loss accounts for more than 97.5% of the total exergy loss in the rotary valve, and that it is possible to improve the structure of the rotary valve by expanding the flow area by 1.5 times. To verify the method, the cooling temperature and power of a remote two-stage GM-PTC were monitored, with original or optimized rotary valves installed. The experimental results show that compared to the original rotary valve, the optimized rotary valve can improve the cooling efficiency of a GM-PTC by 16.4%, with a cooling power of 0.78 W at 4.2 K.</p>