Please attach the gerber files and bill of materials of your design for evaluation. In your schematic, you have shown 50 ohms for your Antenna. Did you use matching network components or did you perform impendance matching by modifying the trace layout?
I finally solved this problem.
This problem seems caused by the oscillator. The frequency of the 37.4MHz oscillator is not accurate enough. I changed one of the load capacitor of the oscillator ,and my circuit works fine now.