下面是一个示例，显示了三个不同的 图标Select。第一个是默认值，第二个是使用 prop 显式覆盖的，第三个利用自定义主题中指定的默认图标 prop 覆盖。主题的创建与您问题中的示例没有什么不同，只是IconComponent指向导入的图标组件 ( AssignmentReturnedIcon) 而不是字符串。

import React from "react";
import {
  makeStyles,
  createMuiTheme,
  ThemeProvider
} from "@material-ui/core/styles";
import InputLabel from "@material-ui/core/InputLabel";
import MenuItem from "@material-ui/core/MenuItem";
import FormControl from "@material-ui/core/FormControl";
import Select from "@material-ui/core/Select";
import AssignmentReturnedIcon from "@material-ui/icons/AssignmentReturned";
import ArrowDownwardIcon from "@material-ui/icons/ArrowDownward";

const theme = createMuiTheme({
  props: {
    MuiSelect: {
      IconComponent: AssignmentReturnedIcon
    }
  }
});
const useStyles = makeStyles(theme => ({
  formControl: {
    margin: theme.spacing(1),
    minWidth: 120
  },
  selectEmpty: {
    marginTop: theme.spacing(2)
  }
}));

export default function SimpleSelect() {
  const classes = useStyles();
  const [age, setAge] = React.useState("");

  const handleChange = event => {
    setAge(event.target.value);
  };

  return (
    <div>
      <FormControl className={classes.formControl}>
        <InputLabel id="demo-simple-select-label-default">Default</InputLabel>
        <Select
          labelId="demo-simple-select-label-default"
          id="demo-simple-select-default"
          value={age}
          onChange={handleChange}
        >
          <MenuItem value={10}>Ten</MenuItem>
          <MenuItem value={20}>Twenty</MenuItem>
          <MenuItem value={30}>Thirty</MenuItem>
        </Select>
      </FormControl>
      <ThemeProvider theme={theme}>
        <FormControl className={classes.formControl}>
          <InputLabel id="demo-simple-select-label-themeicon">
            Explicit Prop
          </InputLabel>
          <Select
            labelId="demo-simple-select-label-themeicon"
            id="demo-simple-select-themeicon"
            value={age}
            onChange={handleChange}
            IconComponent={ArrowDownwardIcon}
          >
            <MenuItem value={10}>Ten</MenuItem>
            <MenuItem value={20}>Twenty</MenuItem>
            <MenuItem value={30}>Thirty</MenuItem>
          </Select>
        </FormControl>
        <FormControl className={classes.formControl}>
          <InputLabel id="demo-simple-select-label-expliciticon">
            Theme Prop
          </InputLabel>
          <Select
            labelId="demo-simple-select-label-expliciticon"
            id="demo-simple-select-expliciticon"
            value={age}
            onChange={handleChange}
          >
            <MenuItem value={10}>Ten</MenuItem>
            <MenuItem value={20}>Twenty</MenuItem>
            <MenuItem value={30}>Thirty</MenuItem>
          </Select>
        </FormControl>
      </ThemeProvider>
    </div>
  );
}