<PAGE>
 
                                                                      Exhibit 11

                     COMPUTER NETWORK TECHNOLOGY CORPORATION

   Statement Re: Computation of Net Income (Loss) Per Basic and Diluted Share
                      (in thousands, except per share data)
                                   (Unaudited)

<TABLE>
<CAPTION>
                                                Net Income   Weighted Average   Per Share
                                                  (Loss)    Shares Outstanding   Amount
                                                ----------  ------------------  ---------
<S>                                             <C>         <C>                 <C>
THREE MONTHS ENDED JUNE 30,

1998:
    Basic                                        $   870           22,107         $ .04
    Dilutive effect of employee stock purchase                                    
    awards and options(1)                           --                150           -- 
                                                 -------          -------         -----
    Diluted                                      $   870           22,257         $ .04
                                                 =======          =======         =====
                                                                                  
                                                                                  
1997:                                                                             
    Basic                                        $  (857)          22,820         $(.04)
    Dilutive effect of employee stock purchase                                    
    awards and options(1)                           --               --             --
                                                 -------          -------         -----
    Diluted                                      $  (857)          22,820         $(.04)
                                                 =======          =======         =====
                                                                                  
SIX MONTHS ENDED JUNE 30,                                                         
                                                                                  
1998:                                                                             
    Basic                                        $ 1,239           22,080         $ .06
    Dilutive effect of employee stock purchase                                    
    awards and options(1)                           --                143           --
                                                 -------          -------         -----
    Diluted                                      $ 1,239           22,223         $ .06
                                                 =======          =======         =====
                                                                                  
                                                                                  
1997:                                                                             
    Basic                                        $  (480)          23,132         $(.02)
    Dilutive effect of employee stock purchase                                    
    awards and options(1)                           --               --             --
                                                                                  
                                                 -------          -------         -----
    Diluted                                      $  (480)          23,132         $(.02)
                                                 =======          =======         =====
                                                                                
</TABLE>

(1)  For the second quarter and first half of 1998, potential dilutive
     securities primarily consisting of outstanding stock options and shares
     issuable under the employee stock purchase plan are included in the
     computation of diluted net income per share using the treasury stock
     method. For the second quarter and first half of 1997, employee stock
     options and shares issuable under the employee stock purchase plan are not
     included in the computation of diluted net (loss) per share due to their
     anti-dilutive effect.