Now I have installed the Gentoo on my MBP succesfully,I need to record some issues that I have solved.

localhost ~ # lspci
00:00.0 Host bridge: Intel Corporation 2nd Generation Core Processor Family DRAM Controller (rev 09)
00:01.0 PCI bridge: Intel Corporation Xeon E3-1200/2nd Generation Core Processor Family PCI Express Root Port (rev 09)
00:01.1 PCI bridge: Intel Corporation Xeon E3-1200/2nd Generation Core Processor Family PCI Express Root Port (rev 09)
00:16.0 Communication controller: Intel Corporation 6 Series/C200 Series Chipset Family MEI Controller #1 (rev 04)
00:1a.0 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Universal Host Controller #5 (rev 05)
00:1a.7 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Enhanced Host Controller #2 (rev 05)
00:1b.0 Audio device: Intel Corporation 6 Series/C200 Series Chipset Family High Definition Audio Controller (rev 05)
00:1c.0 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 1 (rev b5)
00:1c.1 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 2 (rev b5)
00:1c.2 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 3 (rev b5)
00:1d.0 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Universal Host Controller #1 (rev 05)
00:1d.7 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Enhanced Host Controller #1 (rev 05)
00:1f.0 ISA bridge: Intel Corporation HM65 Express Chipset Family LPC Controller (rev 05)
00:1f.2 IDE interface: Intel Corporation 6 Series/C200 Series Chipset Family 4 port SATA IDE Controller (rev 05)
00:1f.3 SMBus: Intel Corporation 6 Series/C200 Series Chipset Family SMBus Controller (rev 05)
01:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI Whistler [AMD Radeon HD 6600M Series]
01:00.1 Audio device: Advanced Micro Devices [AMD] nee ATI Turks HDMI Audio [Radeon HD 6000 Series]
02:00.0 Ethernet controller: Broadcom Corporation NetXtreme BCM57765 Gigabit Ethernet PCIe (rev 10)
02:00.1 SD Host controller: Broadcom Corporation NetXtreme BCM57765 Memory Card Reader (rev 10)
03:00.0 Network controller: Broadcom Corporation BCM4331 802.11a/b/g/n (rev 02)
04:00.0 FireWire (IEEE 1394): Agere Systems FW643 PCI Express 1394b Controller (PHY/Link) (rev 08)

03:00.0 Network controller: Broadcom Corporation BCM4331 802.11a/b/g/n (rev 02)

Thought I have followed the directions of the kernel document,but it still can't find the wireless card,after the google search ,it must enable the following options for the kernel

Device Drivers->Broadcom specific AMBA->
                   < *> BCMA Support
                    [*] Support for BCMA on PCI-host bus

And you can find the firmware in the

 ls /lib/firmware/b43/