The diurnal variations of standard metabolism ( SM ) and routine metabolism ( RM ) of Perinereis aibuhitensis were determined in feeding commercial Paralichthys oliveaceus diet at 20 ℃. The worms used in this experiment were collected from seaside of Zhuanghe , Dalian , Liaoning province. Worms were grouped according to the wet body weight [S 0. 50 ?0.05g,M 0.90 ?0. 05g , L 1. 50 ?0. 05g ] . The relation between dry body weight ( W , g) and wet body weight ( W , g) is equivalent to : W = 0. 2168 wt 0. 0548 ( R2 =0.9833, n = 43) . SM and RM were determined under the oxygen determining apparatus by flowing water system whose water was filtered with a salinity of 31 -32. The Winkler method and Nestle method were adopted to study the oxygen consumption rate (R) and the ammonia excretion rate (AE) . By comparing RM with SM , the specific dynamic metabolism (SDA) of P. aibuhitensis was studied. The results were as follows : (1) SM and RM of P. aibuhitensis decreased with the body weight increasing. It can be described as R = aWb , where W is dry body weight , R is oxygen consumption rate , a and b were parameters ( a were 0. 3725 ,0. 2743 , b were -0. 4817 , -0. 5988 respectively) . SM and RM were significantly affected by dry body weight ( F = 16. 449 , P < 0. 001; F = 19. 327 , P < 0. 001) . And AE were significantly affected by dry body weight too ( F =4. 855 ,P = 0. 014 ;F =4. 003 ,P = 0. 028) . 4 (2) Each group had the same changeable rule of standard metabolism. The averages of SM in S 、 M and L groups were 1. 0248 mg?(g?h) -1,0.7285 mg?(g?h) -1 and 0.5019 mg?(g?h) -1 respectively. But it was higher in night than that at day. SM in night of three groups were as 2. 17 ,1. 42 and 1. 87 times as at day. This might be explained as the activity of P. aibuhitensis was correlated with illumination. The AE of S , M ,L in starved state changed little too , because of the starvation threaten the protein in worm tissue was consumed in metabolism at the end of experiment , so the AE was increasing slowly after experiment beginning 18h ,24h ,24h respectively. (3) RM in each group changed more than that of SM in this experiment. The RM of S ,M and L went to the peak after experiment beginning 21 -24h. The peak values of SDA in S ,M ,L were 3. 936 mg?(g? h) -1,1.5222 mg?(g?h) -1and1.2853mg?(g?h) -1 respectively , as 4. 84 ,1. 71 and 2. 29 times as their SM. By comparing the diurnal variations of SM with RM metabolism of three groups of P. aibuhitensis , results showed that SDA of the three groups , started at the same time , namely after feeding 15h , persisted about 12h. The energy expenditure of SDAwere 271. 62 J ?g 1,73.56J ?g 1 and - 70.56 J ?g 1 respectively. The ammonia excretion rates of S ,M ,L in satiation state changed significantly during the experiment. The peak values of the wave of satiation state were 9. 2176μmol?(g?h) 1 ,6. 5935μmol?(g?h) 1 ,2. 6866μmol?(g?h) 1 respectively , as2.82,4.15and1.67times astheirstarvationstate,accordinglythe durations were9h,9h,12h. Thewave of eachgroup were started later than its oxygen consumption rate , and that of S group started after feeding 24h , and M group was 21h , L group was 15h. The wave energy expenditure of S ,M ,L were 0. 9729 J ?g 1 ,4. 9600 J ?g 1 and 4. 0773 J ?g 1 respectively. This paper preliminarily concluded that SDA of P. aibuhitensis decreased with dry body weight increasing , that is , small worms metabolize much more actively than large worms.