This experiment was aimed to investigate the effects of total mixed ration (TMR) with different particle sizes on growth performance, feeding behavior and digestibility and metabolism of mutton sheep, and initially establish a reasonable TMR production standard for large-scale fattening mutton sheep farms. This study included two experiments, and in each experiment, twenty-four healthy weaned male sheep aged about 4 months were selected and weighed (35.4±5.1) kg. They were randomly divided into 4 groups, 6 sheep in each group, and kept in a single column. The experiment used a 4×4 Latin square design to feed four different TMR (mixing time were TMR1:leymus chinensis 20 min, alfalfa 16 min, peanut stalk 12 min, corn silage 5 min; TMR2:leymus chinensis 30 min, alfalfa 24 min, peanut stalk 18 min, corn silage 5 min; TMR3:leymus chinensis 40 min, alfalfa 32 min, peanut stalk 24 min, corn silage 5 min; TMR4:leymus chinensis 50 min, alfalfa 40 min, peanut stalk 30 min, corn silage 5 min, respectively). Each experiment was divided into 4 periods, 15 days in each period. The results showed as follows:1) with the increase of mixing time, Penn state forage and TMR particle separator (PSPS) dry matter contents at level 1 was decreased, levels 2, 3 and 4 were increased, and the particle size of TMR were reduced gradually; the contents of physical effective neutral detergent fiber (peNDF)8.0 and peNDF1.18 were significantly reduced (P<0.01). 2) In experiment 1, the TMR particle sizes had no significant effects on the daily gain and feed/gain of mutton sheep (P>0.05); the TMR particle sizes had no significant effect on the total feeding time of mutton sheep (P>0.05), but had a significant effect on the chewing time and ruminating time of mutton sheep (P<0.05). With the decrease of TMR particle size, the ruminating time and the chewing time were gradually shortening. 3) In experiment 2, TMR with different particle sizes had no significant effects on the apparent digestibility of day matter, organic matter, neutral detergent fiber, acid detergent fiber and crude protein of mutton sheep (P>0.05). TMR with different particle sizes had no significant effect on crude protein intake, manure crude protein content and urine crude protein content (P>0.05). As the TMR particle size decreased, the intake of peNDF8.0 tended to decrease. In conclusion, under the conditions of this experiment, TMR4 is more suitable for fattening mutton sheep. The corresponding mixing time are:leymus chinensis 50 min, alfalfa 40 min, peanut stalk 30 min, and corn silage 5 min. The corresponding dry matter content of the PSPS are:6.00% of level 1, 30.23% of level 2, 44.62% of level 3, 19.15% of level 4, and the corresponding peNDF content are:peNDF8.0 14.67% and peNDF1.18 32.79%.