Hi Xiangjun,
I added the flash algorithms as you said. But somehow the address shown is a little different from your example (10000000H instead of 00000000H).

With the address 10000000H, I see this error:
Load "debug\\hello_world.out"
No Algorithm found for: 00000000H - 00002D13H
Erase skipped!
Error: Flash Download failed - "Cortex-M4"
When I changed the address to 00000000H, I see this error:
Load "debug\\hello_world.out"
Insufficient RAM for Flash Algorithms !
Erase Failed!
Error: Flash Download failed - "Cortex-M4"
I also noticed the Device Type in my environment says it Ext Flash SPI. In your dialog I see 'On-chip Flash'. The only logical choice for adding algorithm is LPC5460x.
Also, when I looked at the Keil_v5/ARM/Flash directory, here is what I see:

Here I only have one choice for LPC5460x_MT25QL128. So there is no LPC5460x_IAP as you have.
What do you think I should correct?
Thanks.