I intend to use AVR to send a API Command to change the Power Level of Xbee.
I already sent a package
buf_pl[9] = {0x7E,0x00,0x05,0x08,0x01,0x50,0x4C,0x01,0x59} ; // ATPL1
I already checkede the output of AVR through Realterm n the transmitting package was correct.
But Xbee couldnt change its Power Level.
I’m looking forward to getting your helps.
Thank you very much
The problem is with your ATPL1 packet, where the checksum should be 0x0D. Packets with incorrect checksums are ignored, which is why nothing seems to work. The ATWR and ATCN packets are correct.
Hope it helps
Edit: just for the record, the OP has edited the first post to rephrase the question - thus invalidating this reply.
It still cant work. 
I edited my question so 2 above replies are unavailable.
It’s not really a good idea to change the question by editing the first post. It disrupts the logic of the thread and makes it harder for people to see what steps have been taken to try to answer the problem.
All I can say now is that your edited packet is valid. You’ll need to provide more information (in a new addition to the thread) if you want more help. For instance, how do you know the power level hasn’t changed? Or: your packet sets the power level to 1. What was it previously?