<u--input placeholder="輸入積分數量" type='number' inputAlign='right' border="none" clearable
						v-model="countnum" @change="change"  @input="inputNumber">u--input>

change(e) {	
 if(e){
		// 正則表達試
		e = (e.match(/^\d*(\.?\d{0,2})/g)[0]) || null
		// 重新賦值
		this.$nextTick(() => {
			   this.countnum = e
		});
	}
},

或者是

// 只能輸入兩位小數
	inputNumber(e) {
		//正則表達試
		 e = (e.match(/^\d*(\.?\d{0,2})/g)[0]) || null
		
		 //重新賦值給input
		 this.$nextTick(() => {
		    this.countnum = e
		 })
	},