Consumed Host Memory - The % you are seeing for ESXi host is the amount of machine memory used on the host.
Allocated memory includes memory used by the Service Console, the VMkernel, vSphere services, plus the total consumed metrics for all running virtual machines. ( So if you add the Memory allocated to the VM + VMkernal and vSphere Memory = will be total what you are getting in ESXi host window)
Active Guest Memory - The % you are seeing for VM's is the amount of guest “physical” memory actively used.
so vm's not using real memory then If I reduce the amount of memory . i will see Consumed Host Memory size % 50 or % 60 right ? because when i check Active Guest Memory size . it is very low than physical memory . What do you think I should do . because vcenter is sending lots of memory alarms .
Yes , First you need to analysis which VM is configured with high memory and actually utilization is less then required and then you can reduce the memory of guest machine and check.