excelwrite too slow problem

hi: in my code, I need to:

    1. read huge amount of data.
    2. find the data I need.
    3. export to the excel.

so I write a loop:

     for: time step
        read data.
        find data I need.
        export to excel.
     end for

however I found that the excel exporting time is too slow. so I refine the code like this:

     for: time step
        read data.
        find data I need.
        export to excel.
        system('tskill excel')
     end for

    after add the command: system('tskill excel'), the exporting become much faster, and below is the bench mark:

    however I could not open any excel file while running the code.

    so my question is: 
    1. why this could happen? I think the xlswrite will close the excel everytime the writting is end.
    2. is there any way to solve this problem?

thanks! Li